[Basic Photography]
[From the U.S. Government Publishing Office, www.gpo.gov]

TM 1-219
V7 j.35 • I
Document Reserve
WAR DEPARTMENT
TECHNICAL MANUAL * BASIC PHOTOGRAPHY July 1,1941
NON-CIRCULATING
NTSU LIBRARY
b 3 f
TM 1-219
C 1
-U.
TECHNICAL MANUAL
BASIC PHOTOGRAPHY
Changes I	WAR DEPARTMENT,
No. 1 J	Washington, March 6, 1943.
TM 1-219, July 1, 1941, is changed as follows:
401. Distribution of products.
b.	Regulations classifying and governing restricted photographs are contained in AR 380—5. The unit commander * * * of competent authority.
c.	Rescinded.
d.	The Commanding General of the Army Air Forces requires photographs of general service and public interest to be submitted monthly.
/. All photographs distributed by the Army Air Forces will be marked or stamped on the back: “Official Photograph—-U. S. Army Air Forces.” All copyright privileges *	*	* any official
photograph.
g.	When publication is authorized by proper authority, the credit line must read: “Official Photograph, U. S. Army Air Forces.”
******* [A. G. 062.11 (2-22-43).] (C 1, Mar. 6, 1943.)
405. Photographic files.
*	*	*	*	*	*	*
c. Duties and responsibilities.
*	*	*	*	*	*	*
(6) Army Air Forces regulations govern the titling and identification legend to be used on all negatives by Army Air Forces units and activities. A loose-leaf file * * * records and reports.
* * * * * * * [A. G. 062.11 (2-22-43).] (C 1, Mar. 6, 1943.)
410.	Camera repair.
* * * * * * *
d. Rescinded.
[A. G. 062.11 (2-22-43).] (C 1, Mar. 6, 1943.)
By order of the Secretary of War :
G. C. MARSHALL, Official:	Chief of Staff.
J. A. ULIO,
Major General, The Adjutant General.
516369°—43
U. S. GOVERNMENT PRINTING OFFICE: 1943
*TM 1-219
TECHNICAL MANUAL No. 1-219
WAR DEPARTMENT, Washington, July 1, 1941.
BASIC PHOTOGRAPHY
Prepared under direction of the Chief of the Air Corps ------------------- Paragraphs
Chapter 1.	General----------------------------------------------- 1- 5
Chapter 2.	Elementary photography.
Section I. General--------------------------------------------- 6- 7
II.	Camera operation	and	laboratory technique___________ 8-	10
III.	Essentials in making a	photograph_______________ 11-	16
IV.	Processing___________________________________________ 17-	20
Chapter 3.	Chemistry.
Section I. General----------------------------------------------- 21—	22
II.	Elementary__________________;--------------------- 23- 24
III.	Emulsions___________________________________________ 25-	28
IV.	Developers and theory of development_________________ 29-	37
V.	Fixation_____________________________________________ 38-	56
VI.	Washing negatives and prints_________________________ 57-	61
VII.	Reduction and intensification of negatives__________ 62-	65
VIII.	Toning______________________________________________ 66-	70
IX.	Characteristics of chemicals used in photography___ 71-	91
Chapter 4.	Sensitized materials.
Section I. General_______________________________________________ 92-	93
II.	Physical properties_________________________________ 94-	98
III.	Characteristics_____________________________________ 99—102
IV.	Negative materials---------------------------------- 103-107
V.	Positive materials__________________________________ 108-114
VI.	Special emulsions___________________________________ 115-116
VII.	Safelights_____________________________________________ 117
Chapter 5.	Optics.
Section I. Properties of light__________________________________ 118-120
II.	Application of light________________________________ 121-137
Chapter 6.	Filters.
Section I. General---------------------------------------------- 138-143
II.	Nature of color____________________________________ 144-145
III.	Application________________________________________ 146-151
Chapter 7.	Sensitometry.
Section I. General_______________________________________________152-154
II.	Sensitometers______________________________________ 155-156
III.	Development________________________________________ 157-159
IV.	Density determinations------------------------------ 160-162
V.	Contrast determinations_____________________________ 163-167
VI.	Measurement of sensitivity__________________________ 168-171
VII.	Application________________________________________ 172-173
Chapter 8. Ground camera photography.
Section I. General---------------------------------------------- 174-176
II.	View camera________________________________________ 177-180
III.	Hand camera________________________________________ 181-187
IV.	Composition_________________________________________ 188-190
*This manual supersedes TM 2170-5, March 1, 1930.
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Chapter 8.	Ground camera photography—Continued.	Paragraphs
Section V. Exterior subjects__________________________________ 191-192
VI.	Interior subjects________________________________ 193-199
VII.	Identification photographs_______________________ 200-205
VIII.	Photography of moving objects____________________ 206-211
IX.	Flashlight photography___________________________ 212-218
X.	Exposure----------------------------------------- 219-225
Chapter 9.	Negative making.
Section I. General________________________________________________ 226
II.	Exposure----------------------------------------- 227-234
III.	Development______________________________________ 235-242
IV.	Mechanics of development__________________________ 243-247
V.	Fine-grain development___________________________ 248-252
VI.	Negative making in tropical climates_____________ 253 254
VII.	Speed processing_________________________________ 255-264
VIII.	Duplication of negatives_________________________ 265-267
IX.	Defects in negatives____________________________ _ 268-269
X.	Hand work on negatives__________________________ 270-272
XI.	Lettering or titling________________________ _ 273-274
Chapter 10.	Printing.
Section I.	General__________________________________________ 275—278
II.	Contact printing_________________________________ 279- 292
III.	Projection printing_______________________________ 293-297
IV.	Finishing prints---------------------------------- 298-305
V.	Mounting prints___________________________________ 306-315
VI.	Print defects_____________________________________ 316-340
Chapter 11.	Copying.
Section I.	General___________________________________________ 341-342
II.	Mosiac copying----------------------------------- 343-349
III.	Camera-------------------------------------------- 350-353
IV.	Technique----------------------------------------- 354-357
Chapter 12.	Lantern slides and film slides.
Section I. General____________________________________________ 358-361
II.	Glass plates-------------------------------------- 362-366
III.	Film slides______________________________________ 367-372
IV.	Color transparencies______________________________ 373-375
Chapter 13.	Color photography.
Section I. General____________________________________________ 376-377
II.	Methods of reproduction___________________________ 378-379
III.	Illumination_____________________________________ 380-382
IV.	Exposure and development__________________________ 383-385
V.	Application-------------------------------------- 386-388
Chapter 14.	Laboratory operations.
Section I. Functions within the	unit__________________________ 389-393
II.	Materiel------------------------------------------ 394-398
III.	Operation_________________________________________ 399-419
Page
Appendix I. Formulary_________________________________________________ 303
II.	List of chemicals_______________________________________ 314
III.	Tables used in photography______________________________ 320
IV.	Glossary of terms___________________________________•	325
Index------------------------------------------------------------”	335
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BASIC PHOTOGRAPHY
Chapter 1
GENERAL
Paragraph
Definition----------------------------------------------------------- 1
Purpose and scope____________________________________________________ 2
References__________________________________________________________  3
Photographic units___________________________________________________ 4
Responsibility for photographs_______________________________________ 5
1.	Definition.—Photography is an accurate means of recording information of terrain, individuals, objects, and events. It is also a means of communication. It is a medium of vital importance to the commander in obtaining information of a strategical, tactical, or technical nature.
2.	Purpose and scope.—This manual serves as a reference to basic photographic principles and to the technique of military photography. It includes elementary photography, chemistry, sensitized materials, optics, filters, photographic sensitometry, ground camera photography, negative making, printing, copying, lantern slides, color photography, and laboratory operations.
3.	References.—a. Army Regulations.—Instructions relating to the responsibility for obtaining, handling, storing, and distributing photographs are contained in AR 95-5, 105-255, 105-260, 300-15, 600-700, and 850-65.
I). Field Manuals.—Matters pertaining to photography are contained in EM 1-35, 30-20, and 30-21.
c.	Technical Manual.—Operation and methods incident to the making of aerial photographs and aerial photographic products and their application to various purposes are described in TM 1-220.
d.	Technical Orders.—Information and instruction relative to specific items of Air Corps photographic equipment are set forth in Air Corps Technical Orders. A complete list of Technical Orders giving detailed directions for the operation and maintenance of all standard items of Air Corps photographic equipment is contained in Air Corps Technical Order 00-1.
e.	Air Corps Circulars.—Air Corps Circulars of the 95 series contain additional instructions pertaining to Air Corps photography.
4.	Photographic units.—Tables of Organization provide photographic units for many types of Air Corps organizations. Whereas some units are independent organizations and others are sections of Air Corps tactical or base organizations, all require the services of specially trained technicians.
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5.	Responsibility for photographs.—a. Aerial.—The Air Corps is charged with the responsibility of performing all photographic and cinematographic work from aircraft. To this type of photography is applied the general term “aerial photography.”
b.	Ground.—At stations where Air Corps troops predominate, the Air Corps is responsible for performing the essential ground camera photography that is normally done for the War Department by the Signal Corps.
c.	Procurement.—Responsibility for procurement of photographs is a function of command.
d.	Execution of missions.—Each commander having photographic equipment under his control is responsible for the prompt execution of all photographic missions assigned to his unit.
e.	Photo officer.—A specially trained technician known as a photo officer is a member of the special staff of the commander of each unit having photographic responsibilities. The photo officer acts as an adviser to the commander on all technical and tactical applications of photography. He is charged with the technical proficiency of the photographic laboratory and with the technical training of the personnel detailed to photographic duties.
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BASIC PHOTOGRAPHY
Chapter 2
ELEMENTARY PHOTOGRAPHY
Paragraphs
Section I.	General___________________________________________ 6-7
II.	Camera operation and	laboratory technique________ 8-10
III.	Essentials in	making	a	photograph_____________11-16
IV.	Processing_______________________________________17—20
Section I
GENERAL
Paragraph
Use of equipment____________________________________________________ 6
Attainment of quality_______________________________________________ 7
6.	Use of equipment.—Photographic equipment will be used only by personnel trained in its operation.
7.	Attainment of quality.—The finished photograph is the result of many successive operations. The quality of the final product depends upon the satisfactory completion of each of these successive steps. At all times, the progressive photographer must be the severest critic of his own work. Every negative and print made will be studied in order that the experience gained will result in further improvement.
Section II
CAMERA OPERATION AND LABORATORY TECHNIQUE
Paragraph
General___________________________________________________________________ 8
Principle of the camera_________________________________________________   9
Laboratory processing_____________________________________________________ 10
8.	General.—The making of any photograph involves camera operation, and laboratory work called “processing.”
9.	Principle of the camera.—The camera is a lighttight chamber having at one end a lens and at the other a place to insert a holder containing a film coated with a light-sensitive emulsion (fig. 1). This emulsion consists of a gelatin base in which are incorporated minute grains of a silver halide. The camera is focused on the object to be photographed; the holder, which has been previously loaded in a darkroom with the light-sensitive material, is inserted and the protective slide withdrawn. The shutter of the camera is then opened, allowing the rays of light reflected from the subject to pass through the lens, which forms the rays into an image of the
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subject. This image is projected or impressed upon the film for a period of time called the “exposure time” and the shutter of the camera is then closed. A camera shutter is usually automatic, opening when pressure is applied to the actuating lever and closing automatically at the expiration of the time for which it is set. The exposure time is usually a fraction of a second.
10.	Laboratory processing.—The image registered by the exposure of the emulsion is invisible, or latent, and must be made visible by development so that it can be seen and used. The film must be developed in a darkened laboratory. During development, the exposed crystals of silver halide composing the latent image are changed into metallic silver grains which form the visible image. This image, however, is negative; that is, it is reversed as to light and dark so that whatever is light in the subject appears dark or dense in the negative. Upon completion of the negative, the next step in the process is the production of the positive image in which the light and dark areas correspond to those of the subject. This positive image is the photograph (fig. 2(5)). The process of making positive photographs on paper is called printing and is accomplished on a printing machine. A laboratory, which is illuminated with light to which the paper is not sensitive, is used for the purpose. The negative and sensitized paper are placed in correct relation to each other in the machine. When the machine is operated, white light is transmitted through the negative, registering a latent image within the emulsion of the paper. The exposed sheet of paper is then developed by a process similar to that used to develop the negative.
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Figure 1.—The camera.
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® Negative.	® Positive.
Figure 2.—Negative
and positive images.
Section III
ESSENTIALS IN MAKING A PHOTOGRAPH
Paragraph
General--------------------------------------------------------------- 11
Light----------------------------------------------------------------- 12
Subject--------------------------------------------------------------- 13
Lens and shutter-----------------------------------------------------  14
Camera---------------------------------------------------------------- 15
Emulsion ------.------------------------------------------------------ 16
11.	General.—In order to produce a photograph on paper there must be light, subject, lens and shutter, camera, photographic emulsions, and photographic chemicals.
12.	Light.—Light is a form of radiant energy and travels in straight lines. This is seldom noticeable in daylight, but if light enters a darkened room through a small opening it will travel in a straight beam. This is evidenced by dust particles in the air which reflect light, making it visible. It is this property or reflection of light which makes photography possible since all parts of an object will reflect light in all directions. The number of rays reflected depends upon the reflective power of the object.
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13.	Subject.—Light illuminating a subject is reflected in varying intensities from different areas of the subject. An area of the subject from which an intense light is reflected is called a “highlight,” and one which reflects light of very low intensity is called “shadow.” Those areas reflecting intermediate intensities are known as “halftones.” Light which is not absorbed is reflected, the reflection varying in intensity according to its original intensity and amount of absorption within the subject. It is the function of photography to record these many and varied light intensities of the subject. The photographic recordings also vary according to the colors of the objects composing the subject and the sensitivity of the film to those particular colors. From almost every point of the subject, innumerable rays of light are reflected. These innumerable rays of light in passing through the camera lens are refracted in such a manner that an image of the subject is formed and projected upon the film.
14.	Lens and shutter.—a. A photographic lens is a circular glass or combination of glasses which is so ground that it will project an image. The lens is used in the front part of the camera.
ft- A shutter is a mechanical device that regulates the length of time that light passes through the lens. An iris diaphragm is generally incorporated in the shutter to regulate the amount of light passing through the lens.
15.	Camera.—Essentially, a camera is a lighttight chamber. Its purpose is to exclude all light that does not pass through the lens.
16.	Emulsion.—a. The function of photographic emulsion is to retain the image registered by the action of light. A light-sensitive emulsion is composed of gelatin coating throughout which are distributed minute crystals of a silver halide.
ft. It is not definitely known exactly what change takes place in a photographic emulsion when it is exposed to light. However, it is known that the exposed silver halide crystals are altered in some manner which makes them developable.
(1) The generally accepted theory to explain the effect of light on a silver halide crystal is that during the process of ripening one or more silver sulfide specks are formed on each silver halide crystal. These specks are formed by silver combining with the sulfur which is present in ceitain organic compounds which are found in some types of gela-tin. It is thought that this sulfide speck causes strains in the structure of the silver halide crystal. These strains are such that when light strikes the crystal the speck will concentrate the effects of the light so that a developable nucleus is formed.
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(2) The number of silver halide grains affected by an exposure depends upon the sensitivity of the grains, the intensity of the light striking the emulsion, and the length of time the light is allowed to strike the emulsion.
c. Theory of development.—It has been explained that the effects of light on a silver halide crystal are concentrated in one portion of the crystal to form a developable nucleus. During development the silver is separated from the exposed crystal. This silver is metallic and is in the form of extremely minute particles. When the developing solution surrounding the crystal becomes saturated, the silver begins to deposit on the nucleus of the grain. As development continues, more silver is released from the crystal. This silver first goes into solution and then deposits on the nucleus. This continues until finally a grain of silver of minute size is formed. During development this same change occurs in all the other exposed silver halide crystals which form the latent image. Thus the latent image is changed to a metallic silver image. Since there is no developable nucleus in the unexposed silver halide crystals, the unexposed crystals are not affected by the developer.
Section IV
PROCESSING
Paragraph
Development	of	emulsion______________________________________________ 17
Fixation______________________________________________________________  18
Washing________________________________________________________________ 19
Identification	of	photographs------------------------------------------ 20
17.	Development of emulsion.—The purpose of development is to make the latent image visible. An exposed emulsion bearing a latent image has the same appearance before development as one which has not been exposed. This development is accomplished in a darkroom. As has been explained, the developer will change the silver halide grains which have been rendered developable by the action of the light into grains of metallic silver (fig. 3). When all the developable grains have been changed to metallic silver, development is complete. The time necessary to develop an emulsion varies widely with different types of emulsions and different developing solutions. The time of development is usually not less than 1 minute or more than 30 minutes. At the completion of development, the negative is rinsed and then placed in a fixing bath.
18.	Fixation.—a. Fixation dissolves unexposed silver halide, thereby permitting its removal by washing in water. If an emulsion
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is not fully fixed, some silver halide will not be dissolved and therefore cannot be removed in washing. Silver halide remaining in an emulsion will be affected by light and upon prolonged exposure will become discolored. This discoloration or darkening may be so great as to obliterate completely the image.
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Figure 3.—Developed and undeveloped grains. (2300 X)
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b. The principal ingredient of the fixing bath is sodium thiosulfate, commonly called “hypo.” This chemical changes the halide into silver sodium thiosulfate which is soluble and is removed from the film in the plain water washing that follows the fixing bath. Ordinarily, complete fixation is concluded when the film has remained in the fixing bath twice the length of time that it has taken for the milky appearing silver halide, unaffected during exposure, to disappear and the negative to become transparent. The metallic silver image ordinarily is not affected by the fixing solution. However, if fixation is prolonged or the solution is at a temperature higher than that at which it should be used, the metallic image will begin to bleach.
19.	Washing.—When the film has been completely fixed, the negative is thoroughly washed in water for not less than 20 minutes to remove the thiosulfate of silver and all chemicals of the fixing bath from the emulsion. The negative is then dried and is ready for use.
20.	Identification of photographs.—The identification of a photograph is a responsibility of the cameraman. At the time of processing he must furnish the laboratory technician with the title and data that must be affixed to the negative or print. All photographic personnel must realize that a poorly or an improperly identified photograph is generally valueless and may, in the case of improper identification, be harmful in the proper execution of the mission.
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Chapter 3
CHEMISTRY
Paragraphs
Section I. General_________________________________________ 21-22
II.	Elementary_____________________________________ 23-24
III.	Emulsions______________________________________ 25-28
IV.	Developers and theory of development____________29-37
V.	Fixation________________________________________ 38-56
VI.	Washing negatives and prints___________________ 57-61
VII.	Reduction and intensification of negatives_____62-65
VIII.	Toning__________________________________________66-70
IX.	Characteristics of chemicals used in photography, _ 71-91
Section I
GENERAL
Paragraph
General_______________________________________________________________ 21
Importance of uniform solutions_______________________________________ 22
21.	General.—The greater portion of a photographer’s work consists of processing sensitized emulsions. This involves the use of chemical solutions. In order that these solutions may be used intelligently, a few principles of chemistry are reviewed and the nature of photographic emulsions described. The functions and application of developing solutions and fixing baths, and information regarding the proper temperatures of solutions, the washing of negatives and prints, and the reduction and intensification of negatives are discussed.
22.	Importance of uniform solutions.—Military photographs of high quality can best be secured when all the solutions used in processing are mixed properly and of uniform strength. When the factors or processing remain constant, the photographer is enabled to control the variables of exposure to a much greater degree. It is therefore essential that each laboratory technician mix solutions exactly as stated in the formulas, and employ them in the manner and at the temperature specified. The advantages of uniform developing solutions are as follows:
a.	Facilitate judging of negatives as to exposure and contrast and also for the selection of printing papers.
b.	Aid the printer in judging prints for exposure, contrast, density, and color or tone. The judging of color is especially important as the printer can depend on the color being correct only when the developing solution used is of uniform quality.
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c.	Insure that images will be permanent, not bleached, that the hardening action will be adequate, and that there will be an absence of stains and spots caused by the continuation of development after immersion in the fixing bath.
d.	Lend confidence to and assist the photographer in the processes of toning, reduction, and intensification.
Section II
ELEMENTARY
Paragraph
Classification_____________________________________________________________ 23
Altering compounds_________________________________________________________ 24
23.	Classification.—Chemicals in general are classed as elements or compounds.
a. Elements.—An element may be defined as the simplest form of matter. Carbon is the most common element and is familiar to everyone. Other well-known elements are oxygen, iron, silver, gold, sulfur, hydrogen, mercury, bromine, chlorine, iodine, potassium, and sodium.
1). Compounds.—There are approximately 90 elements and they combine in definite proportions to form great numbers of substances of fixed composition which are termed “compounds.” When matter is not found in definite proportions, the combination is termed a “mixture.” A compound may contain only two or it may contain several elements. If two parts of hydrogen are combined with one part of oxygen, the resultant compound is water designated by the chemical symbol H2O. An example of a compound containing more than two elements is sodium carbonate, which is used frequently as an accelerator in photographic developers. From its chemical symbol Na2CO3, it is seen that sodium carbonate is a compound containing two molecules of sodium, one molecule of carbon, and three of oxygen.
24.	Altering compounds.—The nature of compounds may be changed by means of certain agents, such as light, heat, or electricity, and by the addition of other elements or other compounds. That is, one or more of the elements which form the compound may be released. The released elements may be collected separately or they may combine and form entirely different compounds. The solutions used in photographic work are merely correct combinations of the proper chemicals which will cause desired chemical changes in photographic emulsions. For this reason, before taking up photographic
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formulas and the functions of the different chemicals, photographic emulsions must be considered.
Section III
EMULSIONS
Paragraph
Gelatin__________________________________________________________ 25
Types of silver salts used_______________________________________ 26
Making a bromide emulsion________________________________________ 27
Silver grains____________________________________________________ 28
25.	Gelatin.—a. Gelatin is used to hold the silver halide of photographic emulsions in suspension. While collodion and albumin were formerly used in emulsions to support the silver halide, gelatin proved so far superior to these substances that it has been almost universally adopted and practically all photographic emulsions now contain gelatin.
Z>. Gelatin is a byproduct of packing plants, being obtained principally from the hides, bones, and hoofs of animals. Commercially it comes in the form of a powder, flakes, or in shreds. It is a peculiar substance, dissolving readily in warm or hot water but refusing to dissolve in cold water. If placed in cold water, it forms a jellylike mass, the water apparently being absorbed by or dissolving into the gelatin. If dissolved in warm water, it forms a thin liquid. When this solution cools, it will form into jelly even if the percentage of gelatin which it contains is as little as 1 percent. If the jellied gelatin is heated it will liquefy; if cooled, it will set again. This process may be repeated many times, although with continued repetition the gelatin will lose some of its setting qualities.
c. To make a piece of photographic paper, a film, or plate, liquefied gelatin containing silver halide crystals is spread on a proper base. This coating is, at first, quite thick but will soon dry down to a rather thin hard layer. Evenly dispersed throughout the layer of emulsion are innumerable silver halide crystals. The hardness of the gelatin in different emulsions varies. This is because some gelatin is naturally harder than others and because the hardness of gelatin is sometimes increased by the addition of chrome alum.
26.	Types of silver salts used.—The photo-sensitive compounds found in all emulsions are called silver halides, which are compounds of silver with bromine, chlorine, or iodine. These silver halides are formed by combining silver nitrate with potassium bromide, sodium chloride, and potassium iodide, respectively. Silver iodide is the least susceptible to the action of light and silver bromide is the most
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BASIC PHOTOGRAPHY
susceptible. However, when silver iodide and silver bromide are combined, they form ’a much faster emulsion (more susceptible to the action of light) than when silver bromide alone is used. Emulsions are often referred to according to the type of silver compound they contain, such as chloride, bromide, chloro-bromide, or bromochloride emulsions.
a.	Chloride.—Chloride emulsions are found only on contact printing papers. They usually contain a small amount of silver bromide and often contain a trace of silver iodide. Silver chloride is more readily reduced than silver bromide, which accounts for the fact that the developing time for bromide paper is usually about twice that for chloride paper.
b.	Bromide.—All plates, film, fast projection papers, and most lantern slides are coated with emulsions containing silver bromide. These emulsions usually contain some silver iodide. Bromide emulsions are much more sensitive to light than chloride emulsions, sometimes being as much as 1,000 times faster.
c.	Chloro-bromide or bromo-chloride.—These two terms are synonymous. This emulsion is used on slow lantern slide plates and on bromo-chloride printing paper. This paper can be used (with a weak printing light) for contact printing but is fast enough for projection printing. There is a great variation in speed of the different brands, but a bromo-chloride emulsion may be considered several times faster than a chloride emulsion and several times slower than the average bromide emulsion. The developing time is longer than that for chloride papers and less than that of bromide paper.
d.	Silver iodide.—There is no emulsion in which silver iodide predominates although there is usually some of this chemical present in all bromide emulsions and a small amount in chloride emulsions. Some of the effects of adding silver iodide to emulsions are: first, it is possible to make a faster emulsion by combining silver iodide with silver bromide; second, it increases the contrast; and third, it decreases the tendency of emulsions to chemical fog. When silver iodide is added to a bromide emulsion the sensitivity of the emulsion to the green region of the spectrum is increased.
27. Making' a bromide emulsion.—a. To make a bromide emulsion, part of the gelatin to be used is made into a jelly by the addition of cold water. This jelly is liquefied by heating, and potassium bromide, which has previously been dissolved in cold water, is added. A predetermined amount of silver nitrate is then added to the solution in the absence of light.
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When potassium bromide and silver nitrate are combined in the gelatin, silver bromide and potassium nitrate are formed. Silver bromide is practically insoluble in water while potassium nitrate is soluble.
c.	After al] the ingredients have been added the emulsion may be allowed to jellify. It is then shredded and washed to eliminate the potassium nitrate. In other processes the emulsion is ripened before it is shredded and washed.
d.	There are three methods of ripening (or digesting) emulsions. The simplest is to let the emulsion stand for about 24 hours. A second method is to keep the solution at near boiling temperature for several hours, and a third method is to treat the emulsion with ammonia. When an emulsion is ripened before it is washed the ripening process is inclined to increase the size of the silver halide crystals as well as the tendency of the emulsions to produce chemical fog. However, since the speed of emulsions can be increased greatly by ripening, it is considered that the value of increase in speed of the emulsion outweighs the detrimental effects of the increase in size of the silver halide crystals and the tendency of the emulsion to produce chemical fog.
e.	After the emulsion has been ripened, the part of the gelatin that has been withheld is added to the solution. At this point potassium chrome alum may also be added to regulate the hardness of the gelatin. If it is to be used for orthochromatic or panchromatic films, the sensitizing dye is incorporated in the emulsion at this stage. The emulsion is now ready to coat on paper, cellulosic film base, or glass, depending upon whether printing paper, film, or plate is being made.
/. When first coated, the emulsion is quite thick but when dry, it contracts to a hard, smooth layer, thinner than an ordinary piece of paper.
28. Silver grains.—a. To appreciate the true effect of light and photographic chemicals on photographic emulsions, the individual silver halide crystals must be considered. Although a photographic emulsion is very thin, these crystals are so minute that they lie scattered and apart throughout the emulsion. As a rule in slow emulsions, the crystals are smaller than those in fast emulsions because the faster emulsions are more completely ripened than the slower ones; the ripening process tending to increase the size of the silver halide crystals. In the same emulsion, there is a wide variation in the size of the crystals (fig. 4). In every emulsion, there are many grains of ultra microscopic size but in an ordinary film emulsion,
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those that can be seen through a microscope will average from %oooo t° kisooo °f an inch in diameter. It has been estimated that in a 1-inch square section of an average film emulsion there may be 40 billion silver halide crystals. With such an enormous number, in spite of their minute diameter, they must lie many layers deep in the emulsion.
Figure 4.—Photomicrograph—silver bromide crystals.
b. There is not only a wide variation of the size of the silver halide crystals in an emulsion but they also vary as to shape and opacity. Their shapes are round, oval, triangular, rodlike, and irregular. Most of them are semitransparent but some scattered few are almost opaque. Although neither the shape nor the transparency seems to have any effect on their senstitivity, there are numerous crystals which for some unexplainable reason are much more sensitive to light than are the majority.
c. The usual conception of the exposure of emulsions is that strong light penetrates deep into the emulsion affecting many layers of crystals, while the less intense light affects only the crystals which lie in the outer layers of the emulsion. This is relatively true, but
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these supersensitive silver halide crystals are affected by light of low intensity even though they may lie in the lower layers of the emulsion. Therefore, in examining the shadow detail of a negative or the detail in the highlights of a print, it should be realized that at least part of this detail is formed from silver grains which lie deep in the emulsion. One interesting feature of silver halide crystals is, that if a single crystal is affected by light sufficiently to become developable it will be developed completely into metallic silver.
Section IV
DEVELOPERS AND THEORY OF DEVELOPMENT
Paragraph
Ingredients of developing solutions_____________________________________ 29
Developing agents or reducers___________________________________________ 30
Accelerators___________________________________________________________  31
Alkalies used as accelerators___________________________________________ 32
Restrainers____________________________________________________'________ 33
Keepers_________________________________________________________________ 34
Preservatives___________________________________________________________ 35
Exhaustion of developing solution_______________________________________ 36
Summary----------------------------------------------------------------- 37
29.	Ingredients of developing solutions.—a. The ingredients which compose a developing solution may be classified according to their individual functions as follows:
(1)	Developing agent or agents.
(2)	Keeper.
(3)	Preservati ve.
(4)	Accelerator.
(5)	Restrainer.
b. The most important chemical in any developing solution is the developing agent or as it is often called, the reducer or reducing agent which actually changes the exposed silver halide crystals to metallic silver grains. Practically all developers are either neutral or only slightly acid. If one of these developers were dissolved in water and an attempt made to develop an exposed emulsion in this solution, there would be little or no reduction of the silver halide crystals because the reducer is not active while in an acid or a neutral state. Therefore, with the exception of one developing agent known as diaminophenol hydrochloride, it is customary to add an alkali to all developing solutions. A developing solution containing only a reducing agent and an alkali would not only develop
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too rapidly but would be inclined to reduce some of the unexposed silver as well as the exposed. This would cause chemical fog throughout the emulsion and completely spoil the image.
o. To keep the developer from reducing the unexposed silver and to prevent the chemical action from proceeding too rapidly, a restraining chemical, usually potassium bromide, is added to the solution. The solution would now develop an emulsion in a fairly satisfactory manner but would still oxidize too rapidly, probably cause stains, and would rapidly lose its strength. To overcome these difficulties, another chemical which has an affinity for oxygen is placed in the solution. Sodium sulfite in a developing solution will retard the oxidation of the developing agent. It combines with an oxidized developing agent to form mono-sulfonates and di-sulfonates. These chemical compounds formed are usually colorless. Since they are colorless it should be realized that while an exhausted developing solution is usually yellow or brown it is possible to have a badly exhausted solution which is quite clear. If the above chemicals were added in proper amounts to a quantity of water, they would form a satisfactory developer, providing it were used immediately. The chemical used for this is almost invariably sodium sulfite. However, it is far more practical and convenient to mix developers in advance so that they can be used whenever desired. Some developing agents in solution will not keep unless they are in an acid state. To keep the developer in condition until it is used, a small amount of acid or chemical containing an acid is often included as one of the ingredients of the developing solution.
30.	Developing agents or reducers.—While there are many chemicals that are capable of reducing exposed silver salts to metallic silver, most of them cannot be used because they are inclined to reduce the unexposed as well as the exposed silver salt. There are only a few developing agents in common use although there are many sold under various trade names which are the same or only slight modifications of these standard few. Although any one of these developing agents will develop an exposed photographic emulsion, they have different characteristics and produce different effects. Monomethyl para-aminophenol sulfate (more commonly called metol), hydroquinone, and pyrogallic acid (trioxybenzene) are the three most used developing agents. With amidol and para-aminophenol, the list of developing agents used in the Air Corps is complete. Some of these agents have a higher developing potential than others. This means that one will reduce silver under adverse conditions
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where one of a lower potential would not work properly. Such conditions are encountered when using a developing solution that is below normal temperature or when the solution contains an excessive amount of restrainer. Developing agents having a low potential require a stronger alkali and less restraining chemical than those which have a high potential. Of the commonly used developing agents, metol has the highest developing potential.
a. PyrogaUic acid {pyro).—Pyro, which is used only in negative developers, is made from nutgalls which are obtained from the Orient. It is generally used in combination with metol, but may be used alone. When used with decreased amounts of sodium sulfite it produces a deeply stained image. This is considered desirable by many photographers, especially for developing negatives which have been exposed under adverse light conditions. Increasing the amount of sulfite will eliminate practically all this stain. One reason pyro is used so much for developing negatives is that when a small amount of accelerator is used, negatives of low contrast will be secured while negatives of higher contrast will result when the amount of accelerator is increased. Pyro used as a developing agent will tend to prevent the formation of aerial fog. A developing solution containing only pyro as a reducing agent requires little or no potassium bromide. Sodium carbonate is generally used with pyro as an accelerator, although potassium carbonate will work satisfactorily.
ft. Monomethyl para-amdnophenol sulfate.—This developing agent is derived from coal tar. Its trade names are Metol, Elon, Pictol, and Rhodol. For convenience monomethyl para-aminophenol sulfate is frequently referred to in formulas and photographic literature as metol and that designation will be employed in this manual. When metol is used, the developer must contain a relatively large amount of potassium bromide. Since metol works well with a mild alkali, either sodium carbonate or borax is generally used with it as the accelerator. It is little affected by slight changes in temperature, starts reduction quickly, but produces density slowly. Metol is commonly used in the following types of developing solutions: fine-grain negative developers, with hydroquinone in print developers, in negative developers with pyro, in most motion-picture film developers, and in some lantern slide developers.
c. Hydroquinone or hydrochinon.—This developing agent is derived from benzine. It requires little or no restrainer, is not active at a temperature lower than 55° F, and is inclined to produce fog at temperatures higher than 80° to 85° F. It is nonstaining, develops
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a pure black image, and is inclined to give contrasty results. It is used in combination with metol in paper developers, in most developers for positive motion-picture film, and in many lantern slide developers especially when contrasty slides are desired. In the last two developers, it is often the only devoloping agent used.
d. Diaminophenol hydrochloride or amidol {diaminophenol}.— This is a developing agent which is often used in tropical developing solutions but can be used in developers generally. It produces a grayblack image and is especially suitable for use with bromide papers.
(1) Amidol is the only developing agent with which potassium chrome alum can be used in the developing solution because it is the only agent which requires no alkali for acceleration. A solution containing only sodium sulfite and amidol will make a satisfactory developer, but frequently a small amount of potassium bromide is included as a restrainer.
(2) A developer containing amidol oxidizes rapidly and must be mixed immediately before use. It also will deteriorate rapidly in use.
e. P ara-amvinophenol or par amminophenol hydrochloride.—This agent is seldom used except in tropical developers. Para-aminophenol hydrochloride (trade name, Kodelon) is somewhat superior to para-midopheno] hydrochloride. A developing solution in which para-aminophenol is used as a developing agent requires only a small amount of restrainer. A negative developed in this developer will have a pure black image while the images of prints will be a gray-black color. The rapidity with which a para-aminophenol developer will develop an image decreases rapidly as the solution is being used. This can be prevented by adding, at intervals, small amounts of accelerator to the solution. A developer containing para-aminophenol can be used at high temperatures (90° to 95° F.) without causing chemical fog.
31. Accelerators.—a. The accelerator (alkali) in a developing solution energizes the reducing agent and softens the gelatin of the emulsion. The energy with which the developing agent reduces the exposed silver halides to metallic silver depends largely on the amount of alkali present in the solution. The softening of the gelatin allows the developing solution to penetrate and permeate the pores of the gelatin in sufficient quantities so that it can reduce the crystals of exposed silver halide which lie scattered throughout the emulsion.
6. An inadequate amount of alkali in a developing solution will result in insufficient reaction of the developing agent and insufficient softening of the emulsion resulting in a weak image.
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c. Too much alkali in a developing solution will cause excessive reaction of the reducing agent which will result in high contrast, an increase in density, stains, chemical fog, and excessive softening of the emulsion.
32. Alkalies used as accelerators.—The list below shows the alkalies used as accelerators and the amount of the different alkalies that would be equivalent in strength to 1 ounce of sodium carbonate (anhydrous). The amount of borax, sodium metaborate, and paraformaldehyde is not given because it is impractical to substitute one of these chemicals for the other alkalies listed. Although the relative strengths of these different alkalies are as accurate as possible, it must be understood that a strong alkali will not give exactly the same results as a weak alkali even if allowance is made for difference in strength. It is customary and practical to substitute one form of sodium carbonate for another, such as crystal for anhydrous, and to substitute sodium carbonate for potassium carbonate, and vice versa.
Sodium carbonate (anhydrous)______________________________ 1.00
Sodium carbonate (monohydrated)___________________________ 1.17
Sodium carbonate (crystals)_______________________________ 2.69
Sodium hydroxide__________________________________________ . 75
Potassium hydroxide_______________________________________ 1. 05
Potassium carbonate (anhydrous)___________________________ 1.30
Potassium carbonate (monohydrated)________________________ 1.63
Borax______________________________________________
Sodium metaborate________________________________________
Paraformaldehyde (trioxymethylene)_______________________
a.	Podium carbonate.—This alkali is generally used as an accelerator when pyro is used as a developing agent. It is also used in most metol-hydroquinone developers and sometimes in fine grain and even process developers. As a rule, a milder alkali is used in fine-grain developers and a stronger alkali than sodium carbonate is used in process developers.
b.	Podiv/m hydroxide and potassium hydroxide.—These alkalies are used in process developers when extreme contrast is desired. Sodium hydroxide is used more commonly than potassium hydroxide. Both these chemicals are poisonous and highly caustic. They are usually procured in the form of sticks. When a white encrustation of sodium bicarbonate forms on the sticks it must be scraped away as the encrustation must not be used. When scraping or breaking the sticks, the eyes should be protected by goggles.
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c.	Potassium carbonate.—Potassium carbonate may be used as an accelerator in any formula which specifies sodium carbonate. It is not so uniform in strength as sodium carbonate and is slightly more expensive. For these reasons, it is seldom used as an accelerator.
d.	Borax.—Borax is the mildest alkali in common use in developers and is used only in negative developers. It is especially desirable in fine-grain developers where excessive softening of the emulsion must be avoided. Although a weak alkali, it can be used in very small amounts as an accelerator because it is in the class known as buffer alkalies. This means that only a small portion of the alkali is released at any one time. However, as these small portions are used up, more is released until the reservoir of supply is exhausted. For this reason, developers using borax as an accelerator have the faculty of being able to develop a quantity of emulsions before showing noticeable signs of exhaustion. Ordinarily, it is impossible to dissolve sufficient borax in a solution to take the place of a stronger alkali.
e.	Sodium metaborate.—This alkali (trade name, Kodalk) is similar in its reaction to borax, and while a stronger alkali than borax, it is not so strong as sodium carbonate. It is used only in developers for negatives and it is claimed that its use minimizes the danger of chemical fog and eliminates any possibility of the formation of gas bells. Sodium metoborate or Kodalk should be used only in formulas in which it is specified.
/. Paraformaldehyde {trioxymethylene'}.—This alkali is a solid which contains 30 percent formaldehyde. It is used only in process developers where the most extreme contrast is necessary. A developer containing paraformaldehyde must be used at an exact temperature and will even then exhaust rapidly. However, when properly used, it gives superior results. When in a developing solution, the paraformaldehyde combines with the sodium sulfite to form sodium hydroxide which then acts as an accelerator.
33.	Restrainers.—Potassium bromide, potassium iodide, and sodium chloride are the three chemicals which are generally used as restrainers in developers. Of these three chemicals potassium bromide is the most used. Some reducing agents require more restrainer than others and while there are a few developing solutions used which do not include a restrainer, most developers will not function properly unless one is included as an ingredient.
a.	Ordinarily a developer without a restrainer will act as follows:
(1)	Development will be rapid and inclined to develop an image formed near the surface of the emulsion.
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(2)	Some of the unexposed as well as the exposed silver halides will be reduced. This will show as chemical fog.
(3)	The developed image will be lacking in contrast.
(4)	The emulsion, especially a print emulsion, may show slight yellow stains.
(5)	The tone or color of a print will be a bluish black.
b.	When potassium bromide is added to the developing solution, it is difficult for the developing agent to reduce the exposed silver halides and even more difficult to reduce the crystals which are not exposed. After the potassium bromide has been added, the solution will act as follows:
(1)	Development will be slower, especially in the less exposed areas.
(2)	Chemical fog will be diminished.
(3)	The contrast will be increased because of the greater restraining action in the less exposed areas.
(4)	The probability of stains will be decreased.
(5)	The image of a print will be composed of greenish-black silver although prolonged development will cause the silver to become more nearly black.
c.	Potassium iodide has a much greater restraining action than potassium bromide. It is seldom found in formulas for developers but it is most effective for eliminating chemical fog and abrasion marks in photographic printing papers. Increased amounts of potassium bromide will eliminate a reasonable amount of chemical fog in paper; however, the prints will have a greenish tone, whereas potassium iodide will render bluish-black tones. Sometimes the use of a combination of the two will result in prints pure black in color. As the restraining action of potassium iodide is so pronounced, care must be exercised that an excessive amount is not added to the developer. Its use also necessitates prolonged fixation since silver iodide which forms in the emulsion fixes much slower than silver bromide. Prints developed in a developer containing potassium iodide will stain when inspected in a strong light unless they have been fixed for about 2 minutes.
d.	Sodium chloride is seldom found in formulas for developers, but like iodide, is sometimes used in developers for defective emulsions. It is desirable as an extra restrainer in print developers in that it causes little change in the color of the print.
34.	Keepers.—A solution composed only of a developing agent and water will deteriorate in a length of time varying according to the kind of agent. This deterioration consists of oxidation, which in
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this case is an absorption of oxygen from the air and from the water, and this oxidizing action eventually makes the solution unfit for developing purposes. Developing agents will not oxidize in an acid condition, so a slightly acid chemical is added to the solution. Such a chemical is called a “keeper.” Sodium bisulfite is one of the most common chemicals which perform this action. The three acidified sulfites, sodium metabisulfite, also called pyrosulfite, potassium metabisulfite, and sodium bisulfite are the chemicals usually used as keepers in developers. Citric acid and oxalic acid are also used as keepers.
35.	Preservatives.—The difference between a preservative and a keeper is that a keeper prevents oxidation of the solution until it is used, while the preservative prevents excessive oxidation while it is being used. In one-solution developers, the preservative also acts as a keeper.
a.	Sodium sulfite is the chemical most commonly used as a preservative. In fact there are seldom any chemicals other than sodium sulfite and sodium bisulfite used as preservatives.
6.	By regulating the rate of oxidation of the developing agent, the sulfite not only preserves the developer, but regulates the color of the image and prevents stains and fog. Another characteristic of the preservative is that it prevents excessive softening of the emulsion when it is in high concentration in a developing solution. The action of the preservative in a developer is opposite to that of the accelerator.
c.	When in use in a developing solution, sodium sulfite absorbs oxygen and forms sulfonates. This change also occurs in weak solutions of sodium sulfite and of the anhydrous form upon prolonged exposure to the air. To prevent this, sodium sulfite should be mixed in concentrated solution and should not be procured in large containers.
36	. Exhaustion of developing solution.—As a rule, when a de-veloping solution is exhausted it becomes discolored, gradually turning yellow, brown, or milky. The degree of exhaustion is indicated by the amount of discoloration. The formation of bubbles on the surface of the solution also indicates exhaustion.
a. When development is done by inspection, a noticeable increase over the normal time of the appearance of the image is proof of exhaustion. When the time and temperature method is used for developing, an exhausted developer will cause weak images.
&. It is impossible to state precisely the number of negatives a developing solution will develop as it is dependent upon many factors,
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among which are the dilution of the solution, the amount of exposed silver in each emulsion, and how long a time the developer is subject to oxidation.
37. Summary.—From the above explanation of the functioning of developing solutions and the part each ingredient serves in the functioning of the combined solution, it is evident that a photographic developer must be an accurately balanced solution. An increase in the amount of one ingredient necessitates an increase in the amount of another ingredient or a decrease in the amount of yet another to preserve the balance of the solution. It should be further noted that the dilution of a developing solution has a marked effect on the manner in which it works. Negatives and prints of high quality can be made only when developed in a solution compounded from a formula which has been found suitable for the type of emulsion. This formula should be used as long as it proves satisfactory as it is poor practice to change from one formula to another. There are times, however, when variations in the manufacture of an emulsion, differences in water, or climatic changes will necessitate the modification of the formula or a change to an entirely different formula. These modifications and changes should be avoided as much as possible.
Section V
FIXATION
Paragraph Functions of fixing baths_______________________________ 38
Chemicals used in fixing baths_________________________ 39
Stopping development in fixing baths____________________________________ 40
Making the image permanent______________________________________________ 41
Hardening of emulsion_________________________________________________   42
Preservative in a fixing bath___________________________________________ 43
Plain fixing baths______________________________________________________ 44
Acid fixing baths_______________________________________________________ 45
Acetic acid hardening fixing baths______________________________________ 4G
Boric acid hardening fixing baths_______________________________________ 47
Chrome alum fixing baths________________________________________________ 48
Tropical fixing baths___________________________________________________ 49
Rapid fixing baths______________________________________________________ 50
Time of fixation_______________________________________________________  54
Use of double fixing baths______________________________________________ 52
Capacity of fixing baths________________________________________________ 53
Testing acid hardening fixing baths for exhaustion______________________ 54
Acid rinse bath_________________________________________________________ 55
Supplementary hardening baths___________________________________________ 56
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38. Functions of fixing baths.—a. The three functions of fixing baths are to—
(1)	Stop development.
(2)	Make the image permanent by removing unexposed silver halide.
(3)	Harden the gelatin in the emulsion.
b. The acid in a fixing bath accomplishes the first function, the second is effected by means of a chemical (called the silver solvent) which is capable of removing the unexposed silver halide of the emulsion, and an emulsion hardener or toughener performs the third function.
39.	Chemicals used in fixing baths.—The following chemicals are used to perform the above functions:
a.	Silver solvents.—Sodium thiosulfate and ammonium chloride.
b.	Emulsion hardeners (tougheners}.—Potassium alum (white), (potassium aluminum sulfate), potassium chrome alum (potassium chromium sulfate), and formalin (40 percent solution formaldehyde).
c.	Acids.—Acetic acid, sulfuric acid, boric acid, and acidified sulfite (sodium bisulfite).
d.	Preservatives.—Sodium sulfite and acidified sulfite.
40.	Stopping development in fixing baths.—a. Most of the exposed silver halide in an emulsion is changed into metallic silver during development. When a film is removed from a developing solution, the developer within the emulsion and on its surface will continue developing the remaining exposed silver halide. An emulsion is always rinsed after it is removed from the developing solution and before it is placed in the fixing bath. This removes the surface developer and a considerable portion of that which lies deep in the pores of the emulsion which to a great extent stops development. However, unless an acid rinse bath is used, there is still enough developing solution remaining in the deeper pores of the emulsion that development of the remaining exposed silver halide will continue. This continuation of development shows in the form of irregular areas of added density.
b. The acid in a fixing bath will immediately neutralize the alkali of the developer which is retained in the emulsion when it is placed in the fixing solution. As a developer will not oxidize in an acid state, there can be no continuation of development. By preventing oxidation of the developer, the acid will also assist in preventing oxidation stains in the emulsion.
41.	Making the image permanent.—a. Ordinarily when an emulsion is exposed, there is a considerable portion of the silver halide
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unexposed. The amount of unexposed silver halide in an exposed emulsion depends upon the nature of the subject and the amount of exposure. In many instances, the number exposed is less than half of the total crystals in the emulsion. Besides these unexposed silver halide crystals, there is usually a considerable portion of the exposed silver halide in a developed emulsion which has not been reduced to metallic silver by the developer.
b.	This surplus silver halide eventually will become discolored by exposure to light and the quality of the photograph will deteriorate. Therefore, before any photographic image can be considered permanent, all of the unused silver halide and exposed silver halide must be removed from the emulsion.
c.	Silver halides whether exposed or unexposed are insoluble in water. Before they can be washed from an emulsion, they must be treated with some chemical which will form a soluble compound of silver. The chemical generally used to create this change is sodium thiosulfate which changes the undeveloped silver salts to complex silver salts of silver sodium thiosulfate, which are soluble.
42.	Hardening of emulsion.—a. In the process of development, the gelatin of the emulsion becomes softened by the action of the alkali in the developing solution. As soon as development is completed, it is essential that the emulsion is hardened sufficiently so that it can be fixed, washed, and dried without damage to the emulsion. Without hardening, the emulsion is subject to abrasions, scratches, blisters, frills, reticulation, or even complete melting of the emulsion. Reticulation is the wrinkling of the surface of an emulsion into a network.
b.	This hardening of the emulsion can be secured by placing it either before or after development in a solution which is capable of hardening (or tanning) the gelatin. These solutions are called supplementary hardening baths and the chemical used to harden the gelatin is usually alum.
c.	It is more customary to combine hardening with fixation. Therefore, most fixing baths include some form of alum as a hardening agent.
43.	Preservative in a fixing bath.—a. When an acid is added to a solution of sodium thiosulfate, the acid will decompose the sodium thiosulfate and the solution will liberate sulfite and sulfur. When sodium sulfite is added to the solution, the decomposition will continue but the acid will combine with the sulfite and form new hypo. When too much acid or insufficient sulfite is present in a fixing bath, this reforming of the hypo will not occur and the solution will become
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sulfurous and unusable as will be revealed by the milky appearance of the bath.
b. A. second function of the preservative in a fixing bath is to prevent oxidation of the developer which is carried into the solution. Although the acid in a fixing bath will stop most of the oxidation of this developer, a slow oxidation will take place which will cause stains unless a preservative is included in the solution. Sodium sulfite (or sodium bisulfite) in a fixing bath will combine with oxidized developing agents to form complicated and colorless compounds (mono-sulfonates and disulfonates) and in this manner prevent oxidation stains.
44.	Plain fixing baths.—a. A plain fixing bath is composed of hypo and water. The normal strength is a 25 percent solution. A gallon of 25 percent solution contains about 2 pounds of hypo and will test 68 by hydrometer when the temperature of the solution is 65° F.
b.	A 40 percent solution of hypo will react with silver halides faster than a solution of any lesser or greater strength. Solutions stronger than 30 percent are seldom used because when emulsions are fixed in strong solutions of hypo, the emulsion will blister and frill when placed in the wash water. This occurs more often when the wash water is warm. These defects can be prevented by placing the fixing emulsion in a weaker solution of hypo for 2 or 3 minutes before removing it to the wash water, but this will not prevent a second difficulty which is encountered when concentrated solutions of hypo are used. When light strikes an emulsion which is being fixed in a solution of hypo stronger than 30 percent, an insoluble residue of dichroic silver is deposited on the emulsion.
c.	Because plain fixing baths do not immediately stop development, they are seldom used for fixation except when an acid rinse bath is also used. It is necessary to use plain fixing baths in some of the after treatments given emulsions as when using some bleachers, reducers, and intensifiers. Plain fixing baths are used as the foundation for other types of fixing baths.
45.	Acid fixing baths.—a. An acid fixing bath is a plain fixing bath with the addition of a preservative and an acid but does not contain a chemical to harden the emulsion. A satisfactory acid fixing bath can be made by adding about 4 ounces of sodium bisulfite to 1 gallon of 25 percent hypo solution. A more stable fixing bath can be made by adding to each gallon of 25 percent solution of hypo 3.2 ounces of sodium bisulfite and 1.3 ounces of sodium sulfite.
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Z>. Sodium bisulfite is acidified sulfite, and while the acid content is not great, it is sufficient to assist in stopping development when it is used in a fixing bath. The sulfite prevents oxidation of the developer and the decomposition of the hypo by the acid. Acid fixing baths are more suitable for use with prints than they are for negatives. They are recommended for fixing prints either when it is not necessary that the emulsion of the prints be hardened or when an intermediate hardening bath is used. As the acid content of the acid fixing bath is slight, an acid rinse bath should be used to rinse prints before they are placed in the solution.
46.	Acetic acid hardening fixing baths.—a. An acid hardening fixing bath is the most used type. This solution is used for fixing either prints or negatives.
b. The ingredients of the acid hardener are water, sodium sulfite, acetic acid, and potassium alum (white). The amounts of sodium sulfite and potassium alum are usually equal. An acid hardening bath can be prepared by adding to a 25 percent solution of hypo the desired amount of the acid hardener. The ratio of the acid hardener can be varied to secure any desired degree of hardening, but it is better practice to use the same ratio of hardening solution and vary the amount of alum. Any decided increase in the amount of alum indicated in a formula should be avoided since it is seldom necessary to use more alum but frequently necessary to use less.
47.	Boric acid hardening fixing baths.—a. A boric acid hardening fixing bath consists of a plain fixing bath to which has been added a hardener solution composed of water, sodium sulfite, potassium alum (white), acetic acid, and boric acid.
b. Boric acid in a fixing bath extends the time in which the bath will retain its hardening properties. Any fixing bath will eventually precipitate a sludge of aluminum sulfite. When the sludge appears, the solution must be discarded. By extending the time the solution can be used before sludging occurs, the boric acid prolongs the life of a fixing bath. Boric acid fixing baths will usually remain clear throughout their useful lives or until the time of clearing an emulsion of milkiness is at least double that required with a fresh bath.
48.	Chrome alum fixing baths.—a. Because of their staining action, chrome alum fixing baths cannot be used for prints. As a rule, they are used only under tropical conditions of temperature. In extremely hot weather and especially hot damp weather, it is sometimes found that other types of acid hardening fixing baths do not harden the gelatin sufficiently. Potassium chrome alum has greater hardening action on gelatin than potassium alum (white).
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ft. A chrome alum fixing bath consists of a plain fixing bath to which has been added sodium sulfite, potassium chrome alum, and either sulfuric or acetic acid. Chrome alum fixing baths lose their hardening properties more rapidly than other types of acid hardening fixing baths.
49.	Tropical fixing baths.—While a chrome alum fixing bath will prove quite satisfactory for fixing negatives under tropical conditions, equal or superior results can be obtained by using a boric acid hardening fixing bath, provided the negatives to be fixed are first treated in a hardener rinse solution containing potassium chrome alum and sodium sulfate.
50.	Rapid fixing baths.—a. Ammonium chloride is one of the few chemicals besides hypo which is used as a silver solvent in fixing baths. This chemical is classified as a rapid fixing agent, although when used alone it will not dissolve silver halide as rapidly as hypo. If ammonium chloride is combined with hypo in correct proportion, the combination of fixing agents will react faster than when either is used alone. A bath of this type will fix a negative in about 1 minute, if used at a temperature of 75° F.
ft. An ordinary acid hardening fixing bath will fix a negative in about 1% minutes when heated to 80° F. This rapid fixing bath is more convenient than an ammonium chloride hypo bath and is highly satisfactory for the purpose.
51.	Time of fixation.—Time of fixation varies with different emulsions. Cloride emulsions will fix more rapidly than bromide emulsions and bromide print emulsions will fix faster than most negative film emulsions. It is customary and amply safe to fix films twice as long as it takes them to clear. This assures that the sodium silver thiosulfate has reached a soluble as well as a transparent state.
a. When a photographic emulsion is not thoroughly fixed, it is impossible to wash the unused silver halides from an emulsion and the emulsion will eventually stain and fade. There is also a possibility that the emulsion will not be sufficiently hardened.
ft. When an emulsion is left in a fixing bath for a too long period of time, the solution will bleach out some of the more scattered silver grains. This bleaching action will be most noticeable in the shadow areas of negatives and in the highlights of prints. The loss of a very small amount of shadow detail in a negative will make a decided difference in the quality of a print made from the negative. Likewise a faint loss of highlight detail in a print will lower the quality of the print considerably. Prolonged fixation of emulsions
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will also cause excessive hardening of the gelatin and will prevent prints from taking a high gloss when they are ferrotyped.
52.	Use of double fixing baths.—a. When processing either negatives or prints, the trays or tanks used for fixing baths are considerably larger than those used for the developing solutions. This is necessary because the fixation of emulsions usually requires considerably more time than developing which causes large numbers of negatives or prints to accumulate in the fixing bath. Instead of having one large tray or tank to contain the fixing bath, it is much better practice to use a double bath.
b. The emulsions are removed from the developer, rinsed, and placed in the first fixing bath for the first half of the fixing time. They are then removed to the second bath for the final period of fixing. The neutralizing of the developer and most of the changing of the silver salts into silver thiosulfate is accomplished in the first bath. If this first bath is in good condition, it will probably do 80 or 90 percent of the work done by the two baths. As the first bath does most of the work, it will become exhausted before the second bath shows any signs of exhaustion. The first bath should be discarded, the second bath moved into the position of the first bath, and a fresh first bath mixed for the final stage of the fixing process. The theory of working double fixing baths in this manner is that while the first bath does most of the work, if it does not accomplish its share of fixation the second bath will, because of its freshness, assure complete fixation. I he first bath must not be allowed to become exhausted as there is a chance of securing spotted emulsions caused by continuation of development by oxidation stains.
c. The use of double fixing baths not only assures complete fixation but also makes it easier to keep emulsions in batches which saves time and assures more uniform fixation. This system of fixing emulsions is particularly desirable in quantity production.
53. Capacity of fixing baths.—a. Ordinarily, the capacity of a fixing bath is measured by the number of prints or negatives of a certain size which it can be depended upon to1 fix. This refers to the solvent capacity of the hypo. While the ability of a fixing bath to stop development, to harden the emulsion, and to dissolve the silver should exhaust uniformly, it is not always possible to achieve this in actual practice. For instance, a large number of white background prints would exhaust the fixing power of a bath before its power to harden the emulsion or to stop the development was spent. Several times as many dark prints, such as reproductions of blue prints, would exhaust the hardening power of a fixing bath before the
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fixing power was exhausted. Emulsions rinsed in plain water rinse baths will exhaust the hardening power of a fixing bath much faster than those which have been rinsed in acid rinse baths. However, the hardening properties of boric acid fixing baths are seldom exhausted before the fixing capacity has been reached.
b. A gallon of fixing bath of average concentration should fix about fifty 8- by 10-inch negatives or sixty 8- by 10-inch prints. If an acid rinse bath is used with the prints, the capacity of the fixing bath can be doubled. If an intermediate hardener is used in processing negatives, the capacity of the fixing bath is also increased.
c. While it is good practice to know the tentative capacity of fixing baths and to keep an approximate record of the number of prints or negatives which have been processed in a fixing bath, it must be remembered that the estimated capacity of a fixing bath is an approximation and that when the appearance of a bath indicates that it is becoming exhausted, it should be discarded.
54.	Testing acid hardening fixing baths for exhaustion.— a. There are several simple tests for determining whether a used fixing bath is exhausted. While any one of these tests used singly is not a conclusive test, several used together will indicate its true condition. These tests are—
(1)	Frothiness.—Bubbles will form on a fresh fixing bath when the solution is agitated. However, the bubbles will be comparatively few and of small size and will break rapidly. An exhausted fixing bath will form more and larger bubbles which are hesitant to collapse.
(2)	Milkiness.—A milky bath is exhausted.
(3)	Sludging.—When a milky sludge (aluminum sulfite) forms it indicates exhaustion of the bath.
(4)	Feel.—A fresh fixing bath will feel “grippy” to the fingers while an exhausted bath will have a “slimy” feel.
(5)	Test strips.—These give a comparison of the known time it takes a fresh bath to clear a strip of undeveloped film with the time it takes a used bath to clear a similar strip. When the time for clearing in the used bath is double that of the fresh bath, the solution is exhausted.
(6)	Iodide test.—To 10 parts of the fixing solution to be tested, add 1 part of a 4 percent solution of potassium iodide. If the fixing solution is exhausted a milky precipitate will be formed.
b. The above tests for exhaustion of fixing baths should be considered but in case of doubt as to the usability of a fixing bath, it should be discarded. The cost of the chemicals used to fix a negative is only a fraction of a cent. The cost of fixing a print properly is even a
298620°—41-----3
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smaller fraction of a cent. It is poor economy to take a chance on spoiling several dollars worth of sensitized material by economizing on fixing solution.
55.	Acid rinse bath.—While water is the simplest form of rinse, there is danger that development will continue during the rinse and even after it is placed in the fixing bath. The use of an acid rinse bath prevents these difficulties and increases the capacity of the fixing bath.
a.	A common acid rinse bath, or stop bath, for prints is a Id/a percent solution of acetic acid. When prints are removed from the developer, they can be placed directly into the acid rinse bath. It is better practice to rinse the prints momentarily in water and then place them emulsion up in the acid bath. The prints should be left in the acid rinse bath for at least 5 seconds. If desired, they may be allowed to accumulate for as long as 10 minutes. This will permit the fixing of the prints in batches which not only saves time but will assist in uniform fixing. Provided prints are first rinsed in running water, this bath has a capacity of about sixty 8- by 10-inch prints per 100 ounces of solution. When an acid rinse bath becomes deeply discolored or when bubbles begin to form around the edges of the tray, it should be discarded. If acid rinse baths are used, it is possible to fix from 50 to 100 percent more prints in a fixing bath than when water alone is used for rinsing.
b.	A suitable rinse bath for negatives is a 2^ percent solution of sodium bisulfite which will stop development and help preserve the fixing bath but will not harden the emulsion.
c.	Intermediate hardening baths are more often used than rinse baths for negative emulsions. They are a combination rinse bath and hardening bath. An ounce of potassium chrome alum in 32 ounces of water is a standard solution for an intermediate hardening bath. It is good practice to use a bath of this type in all negative processing, but it is most important that it be used when negatives are developed in developers which are strongly alkaline, especially if the negative is to be fixed in a fixing bath of higher than normal acid content. This hardening solution should also be used when the gelatin is abnormally soft after development. Failure to use an intermediate hardening bath when any of the above conditions prevail will probably result in the formation of gas bells during the process of fixation. Gas bells are caused by too rapid chemical reaction between the alkali of the developer in an emulsion and the acid of a fixing bath. This chemical reaction forms a gas in such quantity that being unable to escape through the pores of the emulsion, it raises the emulsion from its support and forms minute blisters. A solution of chrome alum will
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neutralize the developer in an emulsion to some extent and will harden the emulsion sufficiently that gas bells will not form when the negative is placed in a fixing bath. Negatives should be placed in this bath, agitated for at least 5 seconds, and left in the bath for from 3 to 5 minutes. This bath when mixed is a blue-violet color, and when exhausted is a yellow-green color. Sometimes a used chrome alum rinse bath will precipitate a sludge. When this occurs the bath should be discarded since it is most difficult to remove a deposit of this sludge from the surface of the negative.
56.	Supplementary hardening baths.—®. Whenever the emulsion of prints appear too soft, they should be placed in a supplementary hardening bath. This bath is a dilute solution of the potassium alum hardener solution used in the acid hardening fixing bath. This bath is often used for hardening prints after toning by the redeveloping process which invariably softens the gelatin of emulsions. Prints to be dried by belt dryers are often treated in a supplementary hardener so that indentations of the weave of the cloth belt will not be made in the emulsion. Prints are treated in a supplementary hardener for 5 minutes and washed in three changes of water after removal from the hardener solution.
b. Negative emulsions are seldom treated in supplementary hardening solutions. However, when negative emulsions become softened excessively as they often do from certain processes of intensification and reduction, they can be rehardened with a solution containing water, formalin, and sodium carbonate. When hardened sufficiently, the negatives should be rinsed and fixed for 5 minutes in an acid fixing bath
Section VI
WASHING NEGATIVES AND PRINTS
Paragraph
Importance of sufficient	washing______________________________________ 57
Importance of proper	fixation_________________________________________ 58
Theory of washing_____________________________________________________ 59
Methods of washing____________________________________________________ 60
Hypo test solutions-------------------------------------._____________ 61
57.	Importance of sufficient washing.—a. Negatives and prints must be washed for a considerable time after fixation to wash the chemicals of the fixing bath and the sodium silver thiosulfate from the emulsion. The washing must be prolonged because of the spongelike structure of the gelatin coating. It requires time for the water to permeate and free the emulsion from the chemicals. If these chemicals are allowed to remain in the emulsion from imperfect or insuffi
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cient washing, they will in time act upon the metallic silver image and convert it to one of another color or completely fade or obliterate it.
b. Most film negatives are backed with a layer of gelatin. During the fixation of a negative, the gelatin backing as well as the emulsion becomes impregnated with the fixing solution. This solution also penetrates the fibers of the paper base of prints. A negative or print to be permanent must have all the chemicals of the fixing bath and the soluble silver completely eliminated; it is more difficult to wash the chemicals from the paper base of a print, especially a double weight print, than from the emulsion.
58.	Importance of proper fixation.—a. When an emulsion is properly fixed, the undeveloped silver halides are changed into a soluble compound of silver. A portion of this soluble salt goes into solution with the other chemicals composing the fixing bath and the rest is removed by washing the emulsion in running water.
b. The thickness of the gelatin layer composing the emulsion is decreased by the hardening action of the fixing bath. This facilitates the removal of the chemicals from the pores of the gelatin since it is difficult to wash chemicals from gelatin which is abnormally soft. The emulsion requires proper fixation to be sufficiently hardened.
59.	Theory of washing.—The theory of washing can be explained by following what happens in the washing of one 8- by 10-inch negative. A negative of this size, when removed from a standard fixing bath and placed in a tray of water, will carry about 3 drams of the fixing solution into the wash water. This amount of fixing solution will contain about 40 grains of hypo and a proportionate amount of the other chemicals of the fixing solution. When an emulsion has been washed sufficiently to remove the hypo, these additional chemicals are also eliminated.
a.	When a negative is placed emulsion up in a tray of water, the hypo will diffuse from the emulsion into the water. This action will continue until there is an equal concentration of hypo in the emulsion and in the water immediately above the emulsion surface. The concentrated solution is heavier than water and will lie in layers of different densities. Agitation of the water will equalize the concentration throughout the solution and thereby allow more chemicals to diffuse from the negative into the water. Continually changing the water will lower the concentration of hypo, and the washing is considered complete when there is only %00 of 1 percent solution. However, at least theoretically, each square inch of the emulsion would contain 0.033 milligrams of hypo. An emulsion containing this quantity of hypo would not be permanent. Two additional changes of water
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would reduce the amount of hypo remaining in the emulsion to such an extent that it will be permanent provided it is not subjected to extremely adverse conditions. Therefore, 12 complete changes of water are usually considered sufficient for washing emulsions. A complete change of water may be considered as one which involves a complete draining of the previous water, the use of a reasonable quantity of water at a temperature of 60° to 70° F., leaving the emulsions in the water from 3 to 5 minutes and including at least a slight amount of agitation of the emulsions during that time.
b.	Although negatives and prints could be washed in the above manner using relatively small amounts of water, the necessary time is reduced by using more water, either by washing in a series of changes or by using a continuous flow. It has been proved that one complete change of water removes one-half the undesirable chemicals from a negative or print. A second change of water will eliminate one-half the remaining chemicals and after a third water there will be retained in the emulsion only one-eighth of the original amount of chemicals. This explains the necessity of making the first three washings thorough. When the amount of chemicals remaining in a negative or print emulsion is halved in each successive change of water, at the end of 10 changes there will remain only %024 °f the original amount of chemicals. After 12 changes of water theoretically there would remain in the emulsion only about %ioo °f the chemicals which it contained at the beginning of the washing period. This small fractional part of the chemicals remaining in a negative or print will not have a deleterious effect on the image.
c.	Tests have proved that in washing, it is much more difficult to eliminate chemicals from prints than it is from negatives because the fibers of the paper base tenaciously retain the chemicals. This is more pronounced with double-weight prints than single-weight prints. For this reason the working directions for washing negatives and prints specify a certain time for negatives, a longer time for single-weight prints and a yet longer time for double-weight prints.
60.	Methods of washing.—The following methods of washing are direct applications of the theory of washing:
a.	Washing in trays.—Both prints and negatives are often washed in trays. While washing can be accomplished by using one tray, it is better practice to use two trays, changing the emulsions from one tray to another and emptying the water from each tray each time the emulsions are removed to the other tray. Another method used to wash negatives and prints in trays involves the use of a siphon. The siphon is designed so that when it is attached to the edge of the tray,
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fresh water is fed to the surface, while the heavier chemically contaminated water is siphoned from the bottom. Whichever method is used in washing negatives in trays with running water, the negative should be agitated at intervals.
b.	Washing in tanks.—When tanks are used for washing, negatives are placed in metal frames and suspended in a vertical position in the tank. By this method the chemicals diffuse from the negatives and sink to the bottom of the tank, and if the tank is properly designed the heavier solution drains from the bottom. The metal frames hold the negatives apart, allowing the wash water to be in constant contact with both emulsion and back side of each negative.
c.	Mechanical washers.—The most efficient method of washing prints is to use a mechanical washer which has facilities for spraying fresh water in the top and siphoning the chemically contaminated water from the bottom. The prints to be washed are placed in a cage which is revolved either by the force of the entering water or by a motor. The movement of the cage together with the water spray causes the prints to change their position constantly during the washing time. As fresh water is continually flowing into the tank while the used water is being siphoned from it, a few minutes are required to secure a complete change of water. For this reason, it is advisable to rinse prints in two or three changes of water before they are placed in the washer.
61.	Hypo test solutions.—a. Hypo test solutions are used to test piints and negatives to determine whether they have been sufficiently washed. One method of testing is to remove several prints or negatives from the wash water allowing small quantities of water to drain from them into a few ounces of a weak solution of potassium permanganate. If there is only a trace of hypo in the emulsions, the permanganate solution which is a light pink color will change to a lemon color. If the prints or negatives contain a considerable amount of hypo, the solution will become colorless.
b.	A superior test solution is composed of water, sodium hydroxide, and potassium permanganate. When negatives or prints are allowed to drain into this solution, a trace of hypo will cause the color to change from violet to orange. The presence of more hypo in the water will cause it to change from an orange to a yellowish-green color. About 30 seconds should be allowed for the changes in color to occur. However, the same changes in color will sometimes occur because of the presence of oxidizable organic matter in the water used for washing. To avoid any discrepancy in the test, it is advisable to use distilled water for the solution and mix twice the quantity of testing solution needed for the test. Using one-half the solution, perform the
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test as directed above. If discoloration occurs, it may be caused from either hypo or organic matter in the wash water. To test the water, place an amount of plain tap water equal to the quantity of water drained into the first solution in the second half of the testing solution. If there is discoloration in this second half, it indicates that there is organic matter in the tap water. If no discoloration occurs, it is proof that the discoloration in the original test was caused from hypo. The tap water used should not be taken from the container in which the prints are being washed because there would be no indication of its purity.
c.	The above two methods test the amount of hypo in the water which is only an indication of how much is remaining in the emulsion. There are several tests which can be used to determine the amount of hypo remaining in the emulsion. One of these involves treating the emulsion with a solution containing mercuric chloride and potassium bromide. This test, when accurately performed, will determine the presence of hypo in an emulsion when the amount is as small as 0.005 milligrams per square inch. An even more satisfactory method for testing involves the use of silver nitrate. Experiments have been made which showed that an emulsion apparently free from hypo, when tested in an alkaline solution of potassium permanganate, was proved by the silver nitrate test to contain 0.02 milligrams of hypo per square inch. The silver nitrate test is performed as follows: Process, with the prints to be tested, an unexposed sheet of white photographic paper. (The same weight and size of the majority of prints in bath are used.) After the final wash, cut off a strip of this sheet and immerse it in a 1 percent silver nitrate solution for about 3 minutes.' Rinse the strip and compare, while wet, in subdued daylight or artificial light, with the wet untreated portion. If the hypo has been completely removed, no color difference can be observed. A yellow-brown tint indicates the presence of hypo. However, the presence of hydrogen sulfide or wood extracts in the water supply will sometimes cause the same tinting of the test strip even though the hypo has been eliminated from the emulsion.
d.	Hypo eliminators.—Objections are often made to the use of hypo eliminators in' photography. These objections are based on the fact that it is often as difficult to remove the chemicals of the eliminators, or the compounds which are formed by these chemicals, from the emulsions as it is the hypo and that these chemicals when remaining in emulsion will be equally as harmful as hypo. However, the following two treatments have been found to work satisfactorily:
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(1) First method.—Recommended for negatives. Wash negatives 8 to 10 minutes. Treat in 0.3 percent solution of ammonium hydroxide, using distilled water for mixing for 2 minutes. After this treatment wash for 2 minutes. Although ammonium hydroxide is superior, sodium hydroxide or sodium metaborate can be used at the same percentage strength.
(2) Second method.—Wash double-weight prints for 20 minutes. A shorter washing time can be used for single-weight prints, after which place the prints for 5 minutes in the following eliminator
solution:
W ater______________________________________________10	ounces.
Hydrogen peroxide (3 percent solution)_______________16	ounces.
Ammonia (3 percent solution)_______________________ 3*4 ounces.
Water to make________________________________________32	ounces.
After treatment in the above solution, the prints should be washed for 10 minutes. One gallon of this hypo eliminator is sufficient for treating eighty 8- by 10-inch prints. This eliminator can also be used for negatives providing it is diluted about 1 to 10. Stronger concentration than this will soften and blister negative emulsions.
Section VII
REDUCTION AND INTENSIFICATION OF NEGATIVES
Paragraph
General______________________________________________________________________ 62
Types of negatives	for	treatment____________________________________________ 63
Reduction-------------------------------------------------------------------- 64
Intensification	of	negatives_________________________________________________ 65
62.	General.—Although the photographic technician constantly strives to make perfect negatives, there are many negatives made which must undergo special treatments before they can be satisfactorily printed. These special treatments are known as reduction and intensification.
63.	Types of negatives for treatment.—a. The following types of negatives can be improved by intensification or reduction:
(1)	Flat.
(2)	Foggy.
(3)	Contrasty.
(4)	Dense.
(5)	Thin.
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b. Such negatives are the result of incorrect exposure, improper development, faulty emulsions, or sometimes by either the natural contrast of the subject itself or by the nature of the light in which the negative was made. Of the above types of negatives, some may be improved by intensification while others must be reduced. It is better photographic practice to retake a defective negative than to reduce or intensify it, but there are times when it is impracticable or even impossible to expose a second negative. Before subjecting a negative to either of these treatments, it is recommended to make first the best possible print from the negative. Then in case of damage to the negative in the treatment, a copy negative can be made from the print and this negative used as a substitute.
64.	Reduction.—Reduction is often considered as the opposite of developing because when a negative is reduced the image is chemically dissolved, while in development the image is built up by means of chemicals. The need for reduction varies according to the image characteristics in the negative. There are three types of reducers in general use which will fit almost any need.
a. Subtractive or surface cutting reducers.—This type of reducer is used for flat negatives and principally those which show an excessive amount of shadow detail or fog in the shadows. Theoretically, a surface cutting reducer removes an even layer of silver from the upper part of the image. This removal of a thin layer from the entire surface of an image will reduce the amount of fog and shadow detail and will increase the contrast of the negative. In practice, the reducing action is more apparent in the shadow areas than in the clearer portions, probably because the silver grains are more widely separated in the shadow areas.
(1) Farmer’s reducer.—The most common subtractive reducer is Farmer’s reducer, which consists of a solution of plain hypo to which has been added, immediately before use, a sufficient amount of a strong solution of potassium ferricyanide to change the solution to a deep lemon color. When treated in this solution, the silver is converted by the ferricyanide to silver ferrocyanide, which is dissolved by the hypo in the solution. The solution of ferricyanide may be kept as a stock solution, but the hypo solution deteriorates rapidly after the ferricyanide is added.
(a) When a negative which has been dried is to be treated in Farmer’s reducer, it should first be thoroughly soaked. If it is to be treated after immediate removal from an acid fixing bath, it should first be rinsed in several changes of water. After the negative has been reduced it must be washed for 30 minutes in running water.
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(ft) Probably the most satisfactory use that can be macle of a ferricyanide reducer is to reduce the fog that often shows in the transparent areas of negatives of line drawings. Either slight overexposure or overdevelopment will often cause the lines and letters of these negatives to be slightly foggy. This fog can be completely removed by placing the negative in a solution of Farmer’s reducer which affects the heavier densities more slowly.
(2) Permanganate reducer.—This is a subtractive reducer which is applicable when reducing pyro-stained negatives. A ferricyanide reducer will produce additional stain on a stained image, while a permanganate reducer will reduce the amount of stain in the image as well as reducing the metallic image.
(a) A solution of potassium permanganate has only a very limited power to reduce silver. Such a solution is sometimes used to remove a very slight fog from a negative. For most purposes, sulfuric acid (C. P.) is added to the permanganate solution, greatly increasing its reducing action.
(ft) The emulsion of a negative reduced in a permanganate reducer often becomes highly stained with a brownish stain. This stain can be removed by placing the negative in a weak solution of sodium bisulfite.
(c) When potassium permanganate is used, acidified with sulfuric acid, part of the silver which forms the image is converted into silver sulfate which, being soluble, is washed from the emulsion by the water in the reducing solution. After reduction is complete the negative should be rinsed, treated in a weak solution of sodium bisulfite, and placed either in a freshly made plain or acid fixing bath.
ft. Superproportional reducers.—Superproportional reducers reduce more silver in the highlights of a negative than in either the halftones or the shadows. Having this characteristic, it may be seen that a superproportional reducer reduces contrast. Dense highlights can be reduced with no apparent reduction taking place in the less dense areas of the negative.
(1)	An acidified solution of ammonium persulfate is the only reducer which will reduce in this manner. One theory which has been advanced to explain why an ammonium persulfate reducer will dissolve silver grains which lie together in rather compact masses more than grains which lie apart, is that the silver grains which form the high lights of a negative contain some silver bromide, while the more scattered grains are more nearly pure metallic silver.
(2)	A slightly acidified solution of ammonium persulfate will change the silver composing the highlights of a negative into silver
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sulfate which goes into solution in the reducer in the same manner as it does in a permanganate reducer. However, this silver sulfate, when in solution, speeds up the action of the reducing solution, and if reduction is not controlled, will reduce the halftones and shadows of the negative.
(3)	It is difficult to obtain ammonium persulfate of uniform purity and strength. For this reason, the action of this chemical in reduction is somewhat erratic. Difficulties will be lessened if a good brand of ammonium persulfate is secured in reasonable quantities and in small size containers.
(4)	In using this reducer, the negative should be removed from the solution before the reduction has reached the degree desired as a slight amount of reduction will continue before the action can be stopped. This applies to some degree in using all types of reducers. When removed from the reducing solution, the negative should be rinsed hurriedly and placed for a few minutes in a 2 percent solution of sodium bisulfite or. fixed in a fresh acid fixing bath.
c.	Proportional reducers.—A proportional reducer is one which reduces the silver of a negative in amounts proportionate to the quantity of silver forming the different densities of the negative. Proportional reducers are used to reduce dense negatives which have normal or excessive contrast. Since, when using a proportional reducer, amounts of silver are removed which are proportionate to the different densities, the contrast of the negative is decreased. This decrease in contrast is beneficial in treating negatives having excessive contrast as well as excessive density, but is detrimental when treating negatives of normal contrast. Unless it is necessary to make a large number of prints from a dense negative or it is desired to make projection prints which would require prohibitively long exposures, it is better practice to utilize the extra time in printing a dense negative than it is to reduce it in a proportional reducer.
(1)	One type of proportional reducer is made by combining a subtractive reducer with a superproportional reducer. The subtractive reducer reduces the shadows and also slightly reduces the halftones, while the superproportional reducer reduces the highlights and has little reducing action on the halftones. Such a solution can be made by combining in a solution the proper amounts of potassium permanganate, ammonium persulfate, and sulfuric acid.
(2)	After a negative is treated in this solution it should be hurriedly rinsed, placed in a 1 percent solution of sodium bisulfite for a few minutes, and washed without fixing.
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(3)	Proportional reduction of negatives can be conveniently secured by bleaching a negative in the bleaching solution of a chromium intensifier and only partially redeveloping the image in a dilute metolhydroquinone developer. The developer used should not contain an excessive amount of sodium sulfite. After redeveloping to the desired degree the negative is fixed in an acid fixing bath and washed.
d.	Local reduction.—Local reduction is the reducing of a portion or portions of a negative. It is accomplished by applying the solution to the area to be reduced by means of a wad of cotton or a brush. The negative should be soaked in water and supported on a piece of glass. The solution is applied to the negative carefully to avoid affecting any area which it is not desired to reduce. To prevent the spreading of the solution, the negative should be rinsed often. Local reduction requires considerable practice and skill, but it is well worth while to become proficient in this process because negatives can be greatly improved by its use. Any type reducer .can be used for local reduction, but the ferricyanide reducer is the most satisfactory.
65. Intensification of negatives.—Intensification is a chemical treatment for increasing the density or contrast of a negative. It is most important that before intensification a negative be thoroughly fixed. When there is doubt as to the completeness of the fixation of a negative it should be fixed in a fresh fixing bath for 10 minutes and washed 30 minutes. Since most intensifiers tend to soften the gelatin, it is advisable to harden the negative before it is intensified. This is accomplished by placing it in the following solution:
Formalin (37 percent formaldehyde)______________ 214 drams.
Sodium carbonate (desiccated)___________________73	grains.
Water to make-----------------------------------32	ounces.
Treat the negative for 3 minutes in this solution. Wash the negative for 10 minutes and then immerse it in a 2 percent solution of acetic acid. This acid rinse will prevent uneven action of the intensifier. It is preferable to intensify the negative without drying. Only one negative should be intensified at a time and the negative should be constantly agitated throughout the entire process.
a.	Intensifying solutions.—These solutions may be divided into three types according to the method used to increase the opacity of the silver grains which form the image. The three types are:
(1)	Intensifiers which will cause some metal to combine with each silver grain.
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(2)	Solutions which will change silver grains to a different color. This color must be such (usually brown or red) that paper emulsions will be less sensitive to the light which has passed through the negative.
(3)	Solutions containing nitrate of silver which will cause additional silver to deposit on the original metallic image.
b.	Types of negatives suitable for intensification.—The following types of negatives can be improved by intensification:
(1)	Flat negatives having weak shadow details. A negative of this type would be the result of overexposure and underdevelopment.
(2)	A negative of a flat subject, especially when the subject was illuminated with a flat light. A negative made under these conditions will be lacking in contrast and density.
(3)	A process negative of a line drawing or similar subject which has insufficient density in the denser areas of the negative. This lack of density would be caused by either underexposure or underdevelopment of the negative.
c.	Ingredients used in intensifiers.—Compounds of gold, silver, platinum, lead, copper, uranium, and other metals are used as ingredients in intensifiers. The metal of any of these compounds will combine with the silver grains of a negative to produce a strengthened image. Compounds of mercury, chromium, and silver are the most frequently used.
d.	Intensification action of intensifiers.—In selecting the kind of intensification process to use it should be known that they vary primarily in the degree of intensification, rather than in any marked differences in action. The only differences in action which should be considered are slight variations in the solvent power on the weaker parts of the image. Some of the processes tend to dissolve out the shadows while strengthening the shadow portions, whereas others will build up each density of the negative proportionately to its original density. Each of these two types of reducing action will increase the contrast of the negative.
e.	Mercuric bromide intensifiers.—Mercury intensifiers are used more than any other type. They are most satisfactory but have one weakness in that a negative intensified with mercury is very likely to stain after a few years. When permanence is essential, a chromium intensifier should be used.
(1) The bleacher of a mercuric bromide intensifier is a solution containing mercuric chloride and potassium bromide. A negative to be intensified by this process must be thoroughly fixed and washed. The negative is placed in the solution and left until the black of the image disappears. After the bleaching of the negative is complete,
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it is essential that the chemical of the bleaching solution be completely removed from the emulsion before the negative is treated in a redeveloping solution. This can be accomplished by washing in running water for at least 20 minutes or by placing the negative for a few minutes in three successive baths of weak hydrochloric acid.
(2) The image can be redeveloped in any of the following solutions, each of which gives a different degree of intensification:
(«) A 10 percent solution of sodium sulfite. This solution gives the least intensification, forms an image of doubtful permanency, and gives superproportional intensification.
(&) A weak M. Q. developer. Gives more intensification, image not permanent, inclined to soften gelatin.
(c) 10 percent ammonia. Uneven and superproportional intensification and inclined to soften the gelatin.
/. Mercuric iodide intensifier.—This type intensifier has two distinct advantages: First, it is not necessary that the negative be washed completely before intensification, and, second, intensification can be stopped at any desired point. The single solution mercuric iodide intensifier contains equal parts of mercuric iodide, potassium iodide, and hypo, dissolved in water. This solution can be used repeatedly until exhausted. Should intensification be carried too far, the intensification can be reduced or removed entirely by placing the negative in a 20 percent solution of hypo. This must be done before subjecting the negative to any after-treatment. After the negative has been removed from the intensifying solution, it should be washed for 30 minutes. When permanence is essential, the negative must be placed in a metol-hydroquinone developing solution or a 1 percent solution of sodium sulfide. After either of these treatments, the negative must be thoroughly washed.
g.	Chromium intensifiers.—This type intensifier makes a permanent image. It is desirable because a moderate amount of intensification can be secured by one treatment of the negative. A greater amount of intensification can be secured by repeating the process. However, the process should not be repeated more than once. The bleaching solution contains potassium bichromate, hydrochloric acid, and water. Before being placed in the bleaching solution the negative must be hardened in a formalin hardening solution. After the negative has been thoroughly bleached, it is washed for 5 minutes and then redeveloped in a metol-hydroquinone developer. The developer used must be one which does not contain an excessive amount of sodium sulfite. The redeveloping should be in subdued daylight or artificial light, and will require from 3 to 10 minutes, depending
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upon the degree of intensification desired. After redevelopment the negative is rinsed, placed in a fixing bath for 5 minutes, and then washed thoroughly. Greater intensification can be secured by repeating the process.
h.	Reduction and intensification.—There are negatives which can be improved by treating them in both reducing and intensifying solutions. When both treatments are to be given, it is the best practice to reduce the negative before intensifying it. This double treatment for the whole negative is seldom necessary, but negatives are often both locally reduced and locally intensified.
i.	Local intensification.—A negative can be locally intensified by applying intensifying solutions with a wad of cotton or a brush to the parts of the negative which require intensification.
Section VIII
TONING
Paragraph
General___________________________________________________________________ 66
Sepia toning processes____________________________________________________ 67
Hypo alum toning process-------------------------------------------------- 68
Redeveloping process____________________________________________________   69
Prints suitable for sepia toning------------------------------------------ 70
66.	General.—Toning in photography means changing the color of the black silver forming the image of a motion-picture film, lantern slide, or print. Although the color can be changed to green, blue, red, brown, or shades of these colors by the use of proper solutions, only the chemistry and some of the formulas involved in making sepia prints of black and white prints are included herein.
67.	Sepia toning processes.—Sepia toning processes are divided into two general classifications, direct and indirect. In direct processes, the image of the print is converted directly to silver sulfide which is a sepia or brown color. In indirect processes, the black image is first converted to silver bromide or silver chloride, both of which are a yellowish color. This is called bleaching the print. The yellow silver forming the image is then changed into silver sulfide by placing the print into a solution of sodium sulfide.
68.	Hypo alum toning process.—The hypo alum toning bath is preferable for use when there is sufficient demand for sepia prints.
a.	Advantages of toning prints by the hypo alum method over the bleaching and redeveloping processes are:
(1)	It is easier to secure uniform tones and to match prints made at different times.
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(2)	The prints need not be washed after fixation and may be transferred from the fixing bath directly to the toning bath.
(3)	On the average, prints on chloride or bromochloride paper tone better by this method.
b.	Disadvantages of using the hypo alum method are:
(1)	The bath must be used at a temperature of about 120° F.
(2)	It necessitates the use of a double boiler arrangement to be used satisfactorily.
(3)	The prints must be swabbed after toning.
c.	The hypo alum bath contains hypo, potassium alum (white), sodium chloride, and silver nitrate. Some baths also contain gold chloride and are called hypo alum gold toning baths. New baths will not work until ripened by running through some discarded prints. In actual practice, it is not customary to mix an entirely new bath, the used bath being strengthened when necessary by the addition of some fresh solution. The prints tone in from 7 to 10 minutes, the lighter portions of the prints toning first and the shadows last. When the black has disappeared, the toning is complete and all the silver has been converted to silver sulfide.
69.	Redeveloping process.—This process is preferable when sepia toning is not a daily practice and when the prints to be toned are likely to be printed on different papers. This process gives better results than the hypo alum method with prints made on bromide paper. This is a two-solution process, the first solution containing potassium bromide, potassium ferricyanide, and sometimes aqua ammonia. This bath changes the silver image to silver ferrocyanide which is then changed to silver bromide. After a thorough rinsing, the print is placed in a solution of sodium sulfide which changes the silver bromide to silver sulfide. In the first solution, the prints will bleach in a few minutes and in the second solution they will redevelop in a few seconds.
70.	Prints suitable for sepia toning.—a. It is rather difficult to describe the ideal black and white print for sepia toning. Prints on different papers act differently in toning and there is a difference of opinion as to what color is most desirable in a sepia print. Some photographers prefer what are called cold tones and others, warm tones. Cold sepia tones are brown with a blue or purple tinge and warm sepia tones are brown with a yellow tinge. A true sepia tone, however, is a rich brown having a slightly reddish tinge, the same color as furnished for sepia in water colors or oil paints.
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b. In spite of the diversity of opinion as to the ideal color of sepia prints, the following facts relating to the black and white print can be relied upon:
(1)	The print should be a few shades dark, not because it will bleach in sepia toning, but because a brown image is lighter than a black image.
(2)	If possible, the print should be a trifle contrasty, as the contrast from white to the darkest brown of the sepia print is not so great as from white to the darkest shadow of the black and white print.
(3)	Prints should be fixed in fresh fixing baths. If not completely fixed, they will show degraded whites, especially if toned by the redeveloping process.
(4)	The developer used should have less than the normal amount of potassium bromide.
(5)	Prints should be fully developed, but not forced.
(6)	Papers having a soft contrast are inclined to yield cold sepia tones, and papers having a hard contrast yield warm tones.
(7)	Cold prints (blue-black) give cold sepias.
(8)	Warm prints (those having a green or olive tone) give warm sepias.
(9)	Prints having many dark areas appear better sepia-toned than those having considerable sky or other light areas.
(10)	The subject should be one which would logically appear in a brown color. Portraits, especially those on dark backgrounds, and landscapes, particularly autumn scenes, are appropriate for sepias. A picture of a pile of coal or a snow scene would not be proper in sepia color as coal is naturally black and snow does not have a brown cast.
(11)	Prints to be toned by the redeveloping process should be completely washed. If not, the hypo remaining in the print will combine with the ferricyanide and cause bleaching of the print.
Section IX
CHARACTERISTICS OF CHEMICALS USED IN PHOTOGRAPHY
Paragraph
General__________________________________________________________________ 71
Appearance_________:----------------------------------------------------- 72
Solubilities------------------------------------------------------------- 73
Care in handling--------------------------------------------------------- 74
Solid chemicals---------------------------------------------------------- 75
Liquid chemicals--------------------------------------------------------  76
Percentage solutions----------------------------------------------------- 77
298620°—41----4
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Paragraph
Stock and working solutions_______________________________________________ 78
Temperature of solutions__________________________________________________ 79
Mixing solutions by hydrometer____________________________________________ 80
Photographic formula______________________________________________________ 81
Use of scales_____________________________________________________________ 82
Liquid measure____________________________________________________________ 83
Water suitable for photographic purposes__________________________________ 84
Containers suitable for mixing and storing solutions______________________ 85
Preparations for mixing solutions_____________ __ _______________________ 86
Water for mixing__________________________________________________________ 87
Order of mixing___________________________________________________________ 88
Stirring------------------------------------------------------------------ 89
Filtering_________________________________________________________________ 90
Amount of solution to mix_________________________________________________ 91
71.	General.—The important facts concerning each photographic chemical are correct name, general appearance, solubility, proper method of handling, and proper storage. Some chemicals have several names, but the common name for each should be remembered. Chemicals are supplied properly labeled and are best stored in their original bottles or containers, making sure the label is securely attached to the container. The label often includes terms such as Chemically Pure (C. P.), Commercial, or U. S. P., which indicates the strength or purity of the chemical. A chemically pure chemical is one which is as pure as it is possible to manufacture. A commercial chemical is one of weak strength or not of the highest grade of purity. However, some commercial chemicals are used for photographic purposes.
72.	Appearance.—Some chemicals have distinctive appearances that can be easily remembered, but others have the same general appearance which make obvious the necessity of always keeping all chemicals properly labeled. Distinctive physical characteristics may be peculiar colors or shapes of crystals in the case of solids, or distinctive colors, odors, and apparent heaviness or lightness in the case of liquids.
73.	Solubilities.—A definite amount of a chemical can be dissolved in a given amount of water at a specified temperature. This amount varies with different chemicals, being quite large in the case of some and extremely small with others. The amount that can be dissolved usually increases as the temperature of the water is increased. When all the chemical that can be dissolved has been taken up by the solvent, the solution is a saturated solution. This is the basis of solubility tables. In photographic work, solubility tables
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are based on temperatures at 40° and 70° F. A list of chemicals used in photography which includes their solubilities at the above temperatures is given in appendix II.
74.	Care in handling.—A few of the chemicals used in photography are deadly poisons and many others are slightly poisonous. Still others are caustic or corrosive. All chemicals should be handled with extreme care.
75.	Solid chemicals.—a. A solid chemical may be in the form of a powder, grain, or crystal. A chemical in crystal form contains water of crystallization. An anhydrous or desiccated chemical contains no moisture. A few chemicals used in photography are monohydrated. A monohydrated chemical contains more moisture than a dry chemical but less than it contains in a crystal form. Formulas usually specify the strength of the chemical listed when it is available in more than one form. If a different form is substituted, allowance must be made for the difference in strength of the two chemicals.
b. Some chemicals in the form of crystals will deliquesce or effloresce. A deliquescent chemical is one which absorbs moisture from the air. An efflorescent chemical gives off moisture. As the strength of these chemicals varies according to the amount of moisture they have absorbed or lost, they should be stored in a place where the air is of normal humidity.
76.	Liquid chemicals.—A number of the chemicals used in photography are liquids. Liquid chemicals will sometimes expand with heat sufficiently to cause leakage in their containers. Certain liquid chemicals will solidify at low temperatures. For these reasons, liquid chemicals must not be stored where they will be subjected to extremes in temperature.
77.	Percentage solutions.—Many formulas specify that a certain quantity of a definite percentage solution be used. To make 100 ounces of a percentage solution, weigh out a number of ounces of the chemical equal to the number or percent desired and add water to make 100 ounces of solution. Different quantities can be made by using proportional amounts of chemicals and adding water to proportional amounts. The method for mixing percentage solutions from liquid chemicals is explained in appendix I.
78.	Stock and working solutions.—A stock solution is a concentrated solution; that is, the minimum quantity of water is taken when it is prepared so that when it is used it is diluted with water according to directions. The diluted solution is called the working solution. Solutions are made concentrated in order to save labor in preparation, to economize in the number of containers, and to make
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them stable in storage. A given quantity of a stock solution that must be diluted with water for use will last longer than the same quantity of a solution prepared ready for use. Moreover, the concentrated solution may be cooled or heated to the required working temperature by being diluted with water which is warmer or colder than the stock solution. However, when small quantities of a solution are prepared for immediate use, a working solution is usually made up.
79.	Temperature of solutions.—The directions for using a photographic solution usually state that the solution will accomplish a certain result in a given time at a specified temperature. When the solution is used at a higher temperature, the result will be accomplished in a shorter period of time, while if the solution is used at a lower temperature it will require a longer time to cause the same amount of chemical reaction.
a.	Specified temperatures.— (1) Directions for using developing solutions usually specify temperatures of 65° F. for developers for negatives and 70° F. for developers for prints. There are some print developers for which a temperature of 65° F. is specified.
(2)	The temperature for fixing baths is usually either 65° F. or 70° F., but it is the best practice to use the temperature which coincides with that of the developer.
(3)	Hardening baths, intensifiers, reducers, bleaching solutions, etc., are generally used at temperatures of 65° to 70° F., although the temperature may not be specified.
(4)	Solutions to be used in tropical photography are often used at temperatures as high as 90° or 95° F. These high temperatures can be used only because provision is made for additional hardening of the gelatin of the sensitized emulsions treated in the solutions. Temperatures as high as 85° F. are often used in rapid development and rapid fixation. Emulsions can be treated in solutions of high temperature as they are in the solutions for only short periods of time. The highest temperature at which any solution is used in photography is 120° F., which is the temperature of the hypo-alum toning bath and for making sepia prints. The gelatin of prints properly hardened in the fixing solution will withstand this temperature.
b.	Maintaining temperatu/re.—The best method of maintaining solutions at the correct temperature is to have the room temperature the same as that of the solutions. When this cannot be done, the following may be practiced:
(1) Use larger quantities of solutions.
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(2) Place trays or tanks in utensils containing large quantities of water a few degrees warmer or colder than the temperature of the solution.
80.	Mixing' solutions by hydrometer.—a. Hydrometers measure specific gravity, which is the ratio of the weight of a substance to the weight of an equal volume of water at the same temperature. When a chemical is dissolved in water, the specific gravity is increased. The measurement of specific gravity then presents a simple method of measuring the concentration of a chemical in water. The hydrometer is generally calibrated to indicate specific gravity, but quite often its calibration is intended to indicate the concentration of a definite chemical in water. The most common method of using a hydrometer is to know beforehand the specific gravity of the required concentration and to add a chemical to water until the necessary reading is obtained. A standard temperature is generally used in hydrometer measurements, which should be maintained wherever possible since higher temperatures lower specific gravity and lower temperatures raise it.
ft. Formulas often specify that solutions of hypo, sodium sulfite, sodium carbonate, and other chemicals be mixed to a concentration that will give a specified hydrometer test. While a hydrometer can only be used to test a solution containing one chemical, it is an accurate method of mixing solutions. No consideration need be given as to whether the chemical dissolved is in a desiccated, monohydrated, or crystal form, or as to the degree a chemical has deliquesced or effloresced.
81.	Photographic formula.—To prepare a photographic solution, it is necessary to have a formula for such a solution. This formula may be memorized, but if the solution calls for chemicals in exact amounts, it is not safe to depend upon memory but to have a written copy of the formula as a guide for the operations necessary to prepare the solution. The ingredients and the amounts to be used are stated. Amounts are expressed according to a standard system of weights and measures. The formula to be followed should be for the volume of solution desired and in the system of weights and measures that is to be used. The avoirdupois system of weights and the United States standard liquid measure are often used although many formulas are written in the metric system. Tables of weights and measures are included in appendix III.
82.	Use of scales.—a. Two types of balance scales are available for weighing chemicals. The small size is used for weighing small
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amounts of chemicals, usually not more than a few ounces, while the larger size is used for weighing larger quantities.
b. The spilling of chemicals on parts of scales should be avoided. Scales should be kept dry and clean and in accurate adjustment. The pan or scoop on which the chemicals are placed should be protected by a piece of paper to avoid contamination. A paper of a size which will balance this protecting paper must be placed on the opposite side of the scales. When the paper holding the chemical is emptied it should be folded, with any clinging chemicals inward, and disposed of in such a manner that there is no chance of chemical dust contaminating the air.
83.	Liquid measure.—a. The required quantity of a fluid is measured in a graduated container which has marks on the side indicating the capacity of the vessel and smaller units of liquid measure. The extent of such graduations varies according to the total capacity of the graduate and its design, there being small-sized graduates which are finely divided into fractions of a fluid ounce and larger graduates in which it is not possible to measure less than an ounce or half ounce.
b. Sometimes a formula calls for a certain number of drops in a solution. The ordinary type of eye dropper, procurable at any drug store, is the most convenient device for measuring drops. When using an eye dropper, it should be held in a horizontal position to secure large and uniform drops.
84.	Water suitable for photographic purposes.—a. Water comes in various states of purity, the purest form of which is distilled. Distilled water is not necessary for photographic purposes if the water obtained from natural sources does not contain impurities harmful to photographic work.
b.	The impurities that may be present in various kinds of water are dissolved salts, such as bicarbonates, chlorides, and sulfates of calcium, magnesium, sodium, and potassium. If calcium salts are present in the water and a developer is prepared containing sodium bisulfite or potassium metabisulfite, fine needle-shaped crystals of calcium sulfite will precipitate in the developer while it is standing. This precipitate is harmless and will settle to the bottom, but the developer is nevertheless deprived of sulfite in the amount required to form the sludge. If the developer is agitated, the sludge will cause trouble by settling on the emulsions of the sensitized materials. If iron is present to any great extent, the water should not be used for photographic purposes. Near the ocean, sodium chloride may be present in water, which will exert a restraining
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action in the developer. This may be offset, however, by adjusting the quantities of the other ingredients in the developer.
c.	Dissolved salts often cause trouble by crystalizing on the film of a negative after drying; and although not always visible as crystals to the eye, they detract from the transparency of the negative.
d.	Water may also contain suspended matter in the form of dirt and iron rust, which if not filtered out and allowed to settle, will cause spots on the negatives developed in solutions prepared with it. It may also contain slime consisting of animal or vegetable colloidal matter which cannot be removed by filtering. If such water is used for preparing photographic solutions, the colloidal matter coagulates gradually and settles as a sludge.
e.	Water in some localities contains dissolved gases such as air, carbon dioxide, or hydrogen sulfide.
/. Water may be purified as follows:
(1)	Distillation.—Distilled water should be used for mixing solutions whenever it can be obtained easily. However, a still of adequate capacity is expensive and the process of distillation is slow.
(2)	Boiling.—This coagulates the colloidal matter and changes certain lime salts to an insoluble condition in which they then settle out, while dissolved gases such as air, hydrogen sulfide, etc., are removed. Therefore, unless the water contains an excessive amount of dissolved salts, it is usually sufficient to boil the water and allow it to settle.
(3)	Chemical treatment.—This is the most practical method if large quantities of water are required. The following methods of chemical purification may be used:
(®) Add alum to the water in the proportion of 15 grains to a gallon. This coagulates the slime which carries down any suspended particles and the solution rapidly clears. This method does not remove dissolved salts and the small amount of alum introduced into the water has no harmful effect on the developer.
(5) Add a 10 percent solution of sodium oxalate which precipitates calcium and magnesium salts and coagulates the slime, although the sodium and potassium salts are left in solution.
(c) Hydrogen sulfide can be eliminated from water by adding to each gallon of water 60 grains of lead acetate.
85.	Containers suitable for mixing and storing solutions.— Containers made of the following materials are suitable for mixing and storing solutions: glass, enameled steel, 18-8 molybdenum stainless steel, hard glazed stoneware, and hard rubber. A container of
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a size and shape permitting stirring of the solution without spilling must be selected for mixing. The container used for storing a solution should be of a size that can be completely filled and should have a stopper or suitable cover.
86.	Preparations for mixing solutions.—Before starting mixing operations, check the supply of hot water and chemicals and have the necessary containers, funnels, graduates, stirring rods, thermometer, hydrometer, and scales available for use. All apparatus which is used in mixing operations must be reasonably clean.
87.	Water for mixing.—Most formulas specify the amount and temperature of the water to be used in mixing a solution. In some formulas, only the total amount is given and there is no temperature specified. A sufficient amount of water should be used to insure proper dissolution of chemicals so that very little water need be added after the chemicals are dissolved to complete the amount of solution. Too much water, however, will make stirring difficult.
a.	When a formula does not specify the temperature of the water, it is usually correct to use the water at tap temperature. In other cases, knowledge of the characteristics and quantities: of chemicals to be used must be employed. Pyro must not be dissolved at a temperature of more than 100° F. Temperature of 125° F. is safe for dissolving metol and hydroquinone.
b.	The Fahrenheit temperature scale is commonly used in photography. Another system which is often used is known as Centigrade (C.). On the Centigrade scale, water freezes at 0° and boils at 100°, and on the Fahrenheit the corresponding readings are 32° and 212°. There are definite formulas for use in converting one scale to the other, as follows:
5 O=g(F-32) ^=|c+32
88.	Order of mixing.—a. Unless otherwise stated in the formula, the ingredients called for must be dissolved in the order given. Most formulas list the ingredients in that order. However, it may happen that the order of listing the ingredients does not conform with the order in which they should be dissolved. In such case, the photographer is expected to know the proper order of mixing.
b. The correct order for mixing a developer is as follows:
(1)	Dissolve the preservative first. In the case of metol, dissolve
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only a portion of the sulfite first, dissolve the metol, and then the remainder of the sulfite.
(2)	Make sure that one chemical is dissolved before adding the next. If the carbonate or alkali is added before the crystals of the developing agent are dissolved, the crystals wil] begin to oxidize at the surface and the resulting solution will give fog.
(3)	Mix solutions at as low a temperature as possible.
(4)	Always pour dry chemicals into water and not vice versa.
(5)	When adding water to make the total desired amount of solution, it is always permissible to add cold water.
89.	Stirring.—As a solid is added, the water or solution is stirred thoroughly to expedite its dissolving throughout the solution. The solid is poured in a little at a time and a suitable stirring rod is employed. The kind of rod in ordinary use is made of vulcanized rubber, which is chemical proof. For a large tank, a large stirring rod is necessary which is often made of wood in the form, of a paddle. It is best to coat such wooden paddles with paraffin and to use a paddle for one kind of solution only.
90.	Filtering.—It is not good practice to filter a solution unless it is absolutely necessary, since the process of filtration adds too much air to the solution. It may happen, however, that solutions contain foreign particles which should be removed and this is best done by filtration. The most effective kind of filtering is through filter paper. This comes in circular sheets of different diameters suiting the size of the funnel to be used. To place the paper in the funnel, fold it twice so as to form a quarter section and open one loop and the result is a pointed cone which should be inserted, point downward, in the funnel. The liquid to be filtered is poured into the cone. A less effective method of filtering is through clean cloth such as white muslin, or a good grade of raw absorbent cotton. Solutions used for processing miniature films are often filtered because of the danger of foreign particles causing spots on the negatives, which, even though minute, cause noticeable defects when enlarged.
91.	Amount of solution to mix.—Some solutions used in photography must be used immediately after mixing so that only enough for use should be mixed. Although there are a few solutions which will keep almost indefinitely, it is not considered good practice to mix solutions in quantities which will not be used reasonably soon. Most solutions, especially fixed baths, will have better keeping qualities when stored at temperatures not higher than 70° F.
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Chapter 4
SENSITIZED MATERIALS
Paragraphs
Section I.	General________________________________________ 92-93
II.	Physical properties____________________________ 94-98
III.	Characteristics_______________________________ 99-102
IV.	Negative materials____________________________103-107
V.	Positive materials___________________________ 108-114
VI.	Special emulsions_____________________________115-116
VII.	Safelights_______________________________________ 117
Section I
GENERAL
Paragraph
Properties____________________________________________________ 92
Classification________________________________________________ 93
92. Properties.—This chapter includes a description of the various factors which determine the suitability of sensitized materials for specific purposes. Each type of emulsion has definite photographic and physical properties which have been incorporated in its manufacture to fulfill a particular photographic need. The photographic properties for any sensitized material include color sensitivity, contrast, speed, and graininess. Physical properties refer to antihalation and noncurling features which are functions of the backing, type of base on which the various emulsions are coated, surface texture, and other special properties.
93. Classification.—In general, photographic materials may be classed as either negative or positive. Negative materials refer to those on which a negative image is best obtained. Positive materials are generally used in conjunction with negatives to obtain positive images, although there are special emulsions on which a positive image is obtained directly after exposure to light by direct positive or “reversal” processing. Reversal film, natural color film, and direct positive papers are included in the latter classification.
Section II
PHYSICAL PROPERTIES
Paragraph
Emulsion________________________________________________________ 94
Support for the emulsion________________________________________ 95
Protective coatings____________________________________________ 9(5
Noncurl backing_________________________________________________ 97
Antihalation backing____________________________________________ 98
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94.	Emulsion.—The general physical properties of an emulsion are thickness, melting point, irradiation, and processing effects.
a.	Thickness.—Negative emulsions are usually comparatively thick for the purpose of obtaining satisfactory exposure latitude. Positive emulsions coated on a transparent base are normally thinner and reversal emulsions are much thinner. This is to insure complete highlight exposure throughout the emulsion, producing clean and brilliant pictures. Positive emulsions on paper are extremely thin in order to afford rapid processing of prints and to give a clearly defined image by reflected light.
b.	Melting point.-—Photographic emulsions have a certain degree of hardness which determines the rate of penetration of solutions used in processing. The average melting point of all emulsions is about 105° to 110° F. but some special emulsions have higher melting points. Ordinarily, the highest safe temperature for processing an emulsion is about 20° F. below the melting point to avoid undue softening. Too much hardening will decrease the swelling and consequently the penetration rate of the different processing solutions. For obvious reasons, in hot climates it is necessary to have a higher degree of hardening than normal.
c.	Irradiation.—A photographic emulsion before development is considerably turbid. Thus, when light is incident upon it, there is a considerable amount of internal reflection or scattering of light within the emulsion which causes a spreading of the image thereby lowering its definition. This effect is called “irradiation.” The image spread is proportional to the exposure for a particular emulsion but it is negligible except when the exposure is exceedingly great.
d.	Processing effects.—The gelatin of an emulsion swells to different extents during processing, but on drying, it shrinks to very nearly its original size. This effect is reduced to a minimum if temperatures of the various solutions are normal and constant.
95.	Support for the emulsion.—The material selected as a support for a photographic emulsion must possess several important qualities. It must be photographically inert; that is, unable to cause a deleterious action on the emulsion, on the latent image, or on the silver grains of the developed image. It must also be unaffected by the solutions used in processing. There are many substances which are suitable, but the most common are cellulose derivatives, glass, and paper.
a. Cellulose derivatives (film base).—The most commonly used supports for negative emulsions are composed of cellulose acetate and cellulose nitrate. These materials are especially suitable because
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they are strong, lightweight, transparent, and flexible. Film base of cellulose acetate is most often preferred because of its low inflammability. The thickness of the film base varies according to the type of film and the manner in which it is used. Roll film, for example, must be more flexible than cut film and have a thinner base.
b. Glass.—Glass has been largely superseded by the introduction of cellulosic film, but is still used for special applications where rigidity and absolute freedom from swelling or shrinking are important. Other advantages are that it is practically photographically inert and transparent. However, it has the disadvantages of weight, bulk, fragility, and nonflexibility.
Figure 5.—Cross section of film.
c. Paper.—Paper is an ideal support for prints because it is flexible. opaque, economical, and durable. Photographic papers vary in thickness and surface texture according to their use.
96. Protective coatings.—Additional layers of some substance are often included in the manufacture of photographic materials for
60
EMULSION FtLM*BA3E GElATIN BACKING
OVERCOATING
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protective purposes. Some papers have thin coatings of waterproof lacquer over the base for rapid processing and drying. In order to prevent scratches and abrasions during handling, emulsions are often given a top coating of clear gelatin. The film base of aerial films is often especially prepared to minimize the effect of shrinkage (fig. 5).
97.	Noncurl backing.—An emulsion on film will swell when wet and shrink when dried, producing a strain which causes the material to curl. To prevent this, a gelatin coating is often included on the back of the base which will swell and shrink in the same manner as the emulsion, thereby lessening the effective curl of the material.
98.	Antihalation backing.—Light which passes through an emulsion and into the base at an oblique angle is reflected from the rear surface of the base and reenters the emulsion. This produces a bright halo of light around the image and is called “halation.” It can be prevented by placing some substance on the rear surface of the base which will absorb these light rays. This is accomplished either by dyeing the base gray so that the light is greatly reduced in intensity, or by dyeing the gelatin backing with a color to which the emulsion is not sensitive. The colored backing will absorb light and pre-
61
Figure 6.—Halation.
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vent its reflection into the emulsion. Both of these methods are used, depending upon the type of material and its use. The result is called “antihalation.” (See fig. 6.)
Section III
CHARACTERISTICS
Paragraph
Color sensitivity___________________________________________________________ 99
Speed---------------------------------------------------------------------- 100
Contrast____________________________________________________________________101
Graininess__________________________________________________________________102
99.	Color sensitivity.—Ordinary photographic emulsions are sensitive only to blue, violet, and ultraviolet light. Colored objects therefore are reproduced by an emulsion of this kind in very different values of brightness than those received visually. The addition of various sensitizing dyes to the emulsion extends the range of sensitivity of silver halide. Progressive discoveries of new dyes have increased the range to cover the complete visible spectrum and also the infrared region. By the proper choice of sensitizing dyes, an emulsion can be made sensitive to any particular region of the spectrum, visible or invisible. The sensitized emulsion thus can be manufactured for particular uses in photography. It is possible to make photographic exposures with the aid of light waves on either side of the visible spectrum. The photographic emulsion then is much more versatile than vision in its sensitivity to light. (See fig. 7.)
10-6	)0-4 t^Q j,00 IQ4 1O6 iq8 1Q.0 IQ14-IO18
COSMIC GAMMA X U.V.	I.R	HERTZIAN	RADIO	^LECTR
•	OSCILLATIONS.
,-'4^ISIBLE SPECTRUmX,
V B G Y O R
f''	400	700
•PHOTOGRAPHIC SPECTRUM;
200	300	400	500	600	700	800	900	1200
e- COLORBLIND FILM-J
•------ORTHO Fl LM —--•!
L---PANCHROMATIC FILM---——J
•---- - ■	-------------SPECIAL FlLMS----------------------»
Figure 7.—Photographic spectrum.
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100.	Speed.—a. Emulsion speed is a measure of the sensitivity of the emulsion and determines the exposure necessary to produce the desired image. Speed is a measure of the rate of reduction of silver halide to subhalide. Expressions of speed are not in definite units but are relative to the various emulsions. For example, a common method of expressing speed is to select a slow material and consider its speed as unity. Other materials, then, would be given speed ratings depending upon how much faster or slower they would record an image in relation to the standard.
b. There are many factors which definitely influence the speed rating of an emulsion. The most important considerations in speed determinations are color sensitivity of the emulsion, spectral distribution of the light source, developer, and degree of development.
101.	Contrast.—a. When a photographic emulsion is exposed in a camera, an image is registered. The chemical action of the light on the emulsion varies according to the light intensity. A great amount of light will affect a large number of silver halide particles and conversely a lesser number of particles will be affected by a small amount of light. Highlights are the brightest areas of the subject and create the most exposure on the photographic emulsion. Shadows in the subject produce less exposure. The difference in subject brightness from shadows to highlights is expressed as contrast. Photographically, contrast is that property of a photosensitive emulsion which determines the magnitude of density difference resulting from exposure differences. Figure 8 shows the range of brightnesses in a subject of normal contrast.
b.	Contrast in photography primarily is a function of the emulsion but may be governed by other factors. In general, slow emulsions have high potential contrast and the faster emulsions lower contrast.
c.	Other factors which influence image contrast are specific developers, degree of development, and subject contrast which may be varied with illumination.
102.	Graininess.—a. A photographic image is composed of microscopic particles or grains of silver. With sufficient magnification, the image presents a granular appearance and when highly magnified the individual particles can be seen. The image has a grainy appearance when this granular effect is visible without magnification. The degree of graininess of an emulsion is partially dependent upon the original size of silver halide crystals before development. There is no definite measurement of graininess but it is an expression of comparison. Ordinarily, slow emulsions have fine grain and fast emulsions have coarse grain, with equal development. How-
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64
Figure 8.—Negative and print.
© Negative.	@ print.
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ever, by proper selection of developers it is possible to obtain fine grain with an originally coarse-grain emulsion. Originally fine-grain emulsions then would show proportionally finer grain with the same developer. Coarse grain in an image is generally caused by clumping of individual grains during development. Graininess, then, is largely a result of development. (See fig. 9.)
Figure 9.—-Developed grains of coarse- and fine-grain emulsions.
Z>. The resolving power of an emulsion is a measure of its ability to reproduce fine detail. Coarse-grain emulsions tend to have low resolving power and fine-grain emulsions high resolving power. An emulsion of high resolving power will normally produce a sharply defined image. Resolving power is ordinarily expressed as the number of lines per unit of measurement which the emulsion can satisfactorily reproduce. For example, an emulsion of high resolving power may be capable of satisfactorily recording 100 lines per millimeter. (See fig. 10.)
® Test object.
Figure 10.—Resolving power.
® Enlarged image.
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Section IV
NEGATIVE MATERIALS
Paragraph
Classes of color sensitivity__________________________________________________103
Speed and contrast____________________________________________________________104
Choice of negative emulsions__________________________________________________105
Types________________________________________________________________________106
Identification code___________________________________________________________107
103.	Classes of color sensitivity.—Negative emulsions are divided into four general classifications as to color sensitivity; colorblind, orthochromatic, panchromatic, and infrared emulsions.
a.	A color-blind emulsion (orthonon) is one which is not specifically sensitized to any color but has an inherent sensitivity to blue, violet, and ultraviolet. Color-blind emulsions may be manufactured in speed ratings from ultra-fast to extremely slow, but are usually of relatively slow speed and high potential contrast.
b.	An orthochromatic emulsion is sensitive to ultraviolet and all visible colors except red.
c.	A panchromatic emulsion is additionally sensitized to red. Panchromatic emulsions are subdivided into three main classes of color sensitivity as follows:
(1)	Sensitive primarily to blue but somewhat less to green and red.
(2)	Balanced sensitivity to all visible color (orthopanchromatic).
(3)	Highly sensitive to red, equally sensitive to blue and green (hyperpanchromatic).
d.	An infrared emulsion is not sensitive to green, yellow, or orange, but is particularly sensitive to infrared. (See fig. 11.)
104.	Speed and contrast.—a. The relative speeds of negative emulsions vary over a wide range when used with daylight and even a greater range for artificial light. The emulsions at the extremes of this range are ordinarily used for special purposes. Color-blind emulsions of low speed are generally used in process photography because of their high potential contrast and resolving power. The fast emulsions ordinarily are of hyperpanchromatic sensitivity and are often used for exposures in artificial light because of their high sensitivity to red.
b. The inherent contrast of negative emulsions also varies over a wide range. The slower emulsions generally have higher contrast than the fast emulsions.
105.	Choice of negative emulsions.—The choice of a negative emulsion is governed by the purpose for which it is to be used. Speed
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1.	Human eye sensitivity.
2.	Color-blind emulsion.
3.	Orthochromatic.
4.	Panchromatic.
5.	Infrared.
Figure 11.—Spectrograms—-emulsion color sensitivity.
and color sensitivity are two primary factors to be considered in the choice of a negative emulsion. Emulsions may be divided into four speed classifications, as follows:
a.	Color-blind emulsions are of the slowest negative material class and are especially suitable for copying. They have high resolving power, low graininess, high rate of development, and high potential contrast. A process emulsion is one made especially for the repro-
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2
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5
i	i	।	i	i	i	i
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duction of line work in high contrast. Color-blind emulsions of a higher speed rating than a process emulsion are also widely used in copying when normal contrast is desirable and true color rendition unnecessary.
b.	(1) In general photography when speed is not a factor, a film of moderate speed may be chosen. Moderate speed emulsions are known as commercial emulsions and may be of almost any spectral sensitivity. If color separation is desirable, an orthopanchromatic emulsion should be chosen unless the color separation is such that an orthochromatic emulsion will suffice. Commercial emulsions are also widely used in copying.
(2)	The largest group of emulsions which may be included in a single class are those which are just above the speed of the commercial group. They are practically all of orthochromatic or panchromatic sensitivity. Their speeds cover a wide range from moderate to ultra-fast. Their contrast and development characteristics also cover a wide range, but the initial contrast of any emulsion of this class is considerably lower than that of any film of the commercial type. Films of this type have reasonably high speed, good exposure latitude, acceptable graininess, and satisfactory keeping qualities.
c.	Ultra-fast emulsions are used when speed is the essential. They are usually manufactured only in orthochromatic or panchromatic sensitivity.
d.	Infrared emulsions are made for the purpose of making photographs with the aid of infrared radiations. Aside from the value of infrared photography in medical diagnosis, criminology, biological and botanical research, and many other allied fields, it is invaluable to the aerial photographer as a means of procuring photographs at high altitudes or at great distance from the subject. Infrared radiations readily pass through suspended dust and water vapor in the atmosphere, thus permitting their use with an infrared sensitive emulsion under conditions both impracticable and impossible with other negative materials. An infrared emulsion is characteristically similar to a commercial color-blind emulsion with the exception of its sensitivity to infrared light.
106.	Types.—The different types of negative materials are roll film, cut film, film pack, and plates.
a.	Roll film is of many different kinds, sizes, and color sensitivities. Ordinary roll film is that made for amateur cameras and consists of a strip of film wound on a suitable spool with opaque backing paper. The base is thin for flexibility.
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(1)	Aerial film is a special type of roll film supplied in greater widths and lengths. There is no backing paper on aerial film because of the bulk, but there is an opaque leader on each end of the roll to protect it from light. The base is thicker than that of ordinary roll film because of the large negative size, and it is often especially prepared to have very low shrinkage.
(2)	Motion-picture film is made in long narrow strips with perforations on the sides to allow accurate positioning of successive small portions of the film in the exposure aperture of the camera. There are two standard widths of motion-picture film, 35- and 16-millimeter. The 35-millimeter film is the professional width and is also used extensively for amateur photography with miniature cameras. The 16-millimeter film is used most in amateur movie photography.
b.	Cut films and plates are most widely used in commercial photography. They are available in large sizes and are particularly well-suited for use with professional cameras. Since each negative is a separate piece of film, it can be exposed and developed individually. Emulsions are available in this form to conform to the large variety of applications in commercial photography.
c.	Film packs have an advantage over cut films since they can be loaded into an adapter and the adapter inserted in the camera without the aid of a darkroom. There are generally a dozen sheets of film in a pack. When one has been exposed, it is pulled by a paper tab to the back of the pack and the next sheet is ready for exposure. These sheets can be removed from the pack individually if necessary. In order to obtain flexibility, the base is made thinner than that of cut film. Only the most widely used emulsions are available in pack form. (See fig. 12.)
UNEXPOSED FILM PRESSURE PLATE	PAJPEfi BACKING
PLUSH -Lr	.s'	)
LIGHT TRAP ■ X	SPRING^^^-^^ ^SPRING	1
*fnnn x---	--------------------------------paper tabs^_____________
■■■ -..............— ■■ \ ■ ==
/ END COVER^	EXPOSED
PAPER TABS	F,LM
TORN OFF HERE
Figure 12.—Cross section of film pack.
107.	Identification code.—Cut films of all emulsions are furnished with reference notches near one corner. This is to identify the emulsion surface during loading of the film. When the notches are
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in the upper right corner, the emulsion surface is toward the operator. These notches are also in the form of a code to identify the type of emulsion. Each film manufacturer has a particular code which does not overlap any other. Thus the film can be positively identified as to type of emulsion and emulsion surface while the operator is in total darkness. (See fig. 13.)
Figure 13.—Notching code for cut film.
Section V
POSITIVE MATERIALS
Paragraph
General__________________________________________________________________108
Transparencies___________________________________________________________109
Paper prints--------------------------------------------------------------HO
Speed--------------------------------------------------------------------111
Paper contrast_______________________________________________________    112
Paper bases______________________________________________________________113
Surface texture----------------------------------------------------------114
108.	General.—Positive emulsions differ considerably. In general they have a much finer grain, are slower than negative emulsions, and have somewhat higher contrast. Positives are made on transparent or translucent bases to be viewed by transmitted light, either directly or by projection, or on opaque bases to be viewed by reflection.
109.	Transparencies.—The principal positive materials viewed by transmitted light are motion-picture positives and lantern slide plates or films, both normally used for projection on a screen.
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a.	Motion-picture positive film.—This film is coated with a bromide emulsion. Its speed and color sensitivity compare favorably with a slow process color-blind emulsion of potentially high contrast. Correct exposure and contrast of an emulsion of these characteristics depend very markedly upon the degree of development. The graininess is much lower and the resolving power much higher than that of ordinary negative materials. Motion-picture positive film is used for motion-picture positives, lantern film slides, and to some extent for microcopying work.
b.	Lantern slide plates {glass').—These plates have a bromide emulsion similar to that of positive film. They are available in several grades of contrast. As with negative bromide emulsions, a wide range of contrast can be had by proper manipulation of developer and developing conditions. To further the range of contrast, lantern slides are sometimes coated with a special chloro-bromide emulsion.
110.	Paper prints.—Paper emulsions are of three types; bromide, chloride, and chloro-bromide. These emulsions are made especially thin in order to enhance the reflective ability of the finished print and as an aid to flexibility. They are of fine grain and high resolving power.
111.	Speed .—Positive emulsions cover a very wide range of speed, the chlorides being the slower and the bromides much faster. The speed of chloro-bromide emulsions overlap these two divisions.
a.	Chloride emulsions are generally made for the purpose of direct contact printing. A rapid chloride paper is also made for projection, but is slower than ordinary bromide papers.
b.	Bromide emulsions are made for the purpose of optical or projection printing.
c.	A chloro-bromide emulsion, due to its variance in speed characteristics, may be used for either contact or optical printing. The slower ones are suitable only for contact work while those of more bromide content are chiefly suitable for projection.
112.	Paper contrast.—a. Development.—Owing to the thinness of the coating and fine grain, a paper emulsion develops rapidly. Contrast rapidly increases during the first period of development, but increases more slowly as the shadow density approaches its maximum. Bromide and chloride emulsions should be developed to a standard degree of development which will produce what may be termed normal or “full” development. This development will reproduce the contrast gradations of the negative in their truest relationship, providing an emulsion of the proper inherent contrast is used. Less development than normal will result in uneven contrasts and
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densities. More than normal development will result in a slight contrast and density increase but is generally impractical for the reason of its slight value and may cause serious harm by way of stains. Chloro-bromide emulsions are similar to film emulsions in their reactions to a developer. Developer modifications of ingredients, and time of development, as well as temperature variations may therefore be employed advantageously. Emulsions of this type are capable of producing satisfactory results over a wide range of negative contrasts and are of value in producing special effects such as a control of contrast (to the minimum or maximum) without an appreciable loss of general print quality.
b. Inherent contrast.—Since contrast is only slightly variable by development manipulation, paper emulsions are therefore manufactured with a wide range of inherent contrasts. This wide range of available contrasts increases the acceptable range of negative emulsion contrast. The potential contrast of an emulsion is usually expressed by a number or a descriptive word, the exact method of expression being dependent upon the manufacturer.
113.	Paper bases.—a. Photographic papers are made in varying thicknesses or weights. The three most common are known as lightweight, single weight, and double weight. A lightweight paper may be rolled, bent, or folded without appreciable damage, although treatment of the finished print with a glycerin bath or similar softening agent is usually necessary if the print is to be folded. A single-weight paper is usually the type used for small pictures, including 8- by 10-inch. A double-weight paper is generally used for larger prints to facilitate their handling. It is especially desirable for rough paper surfaces.
b. Most papers are coated with baryta as a support for the sensitive emulsion. Papers of this nature cannot be folded satisfactorily without cracking. The baryta layer is therefore not used when the product is made with the expectation that its use may necessitate folding or sharp bending.
114.	Surface texture.—After paper is surfaced with baryta, it is embossed, producing almost any desired surface effect when the emulsion is coated. Linen, tapestry, matte, semimatte, glossy, and smooth are a few common surface textures. These effects are aided somewhat by the paper texture. Surface texture is most often considered in selection of papers for particular types of photographs. Glossy or smooth surfaces are preferable for small prints or prints wherein maximum detail is desirable. Rough surfaces are
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generally preferred for enlargements. They have the faculty of suppressing excessive fine detail or concealing a lack thereof and also suppressing apparent graininess.
Section VI
SPECIAL EMULSIONS
Paragraph
Reversal----------------------------------------------------115
X-ray_______________________________________________________116
115.	Reversal.—a. A reversal emulsion is made for the purpose of producing a positive image with the same emulsion used as the negative. Upon the completion of development, such an emulsion contains two images, that of the exposed and developed silver in negative relationship to the subject, and that of the unexposed and therefore undeveloped silver. The exposed and developed silver image is eliminated by bleaching, and a second image exposed and developed to form a new image of reversed density values which truly represents the subject.
b. Since nearly all silver halide grains are utilized in this process, the exposure latitude of any emulsion used for reversal purposes is very limited. Emulsions made for the purpose are extremely thin so as to offset the possibility of too great a highlight density caused by the second exposure. Reversal emulsions are often used for colored photography.
116.	X-ray.—Silver halide absorbs only a small portion of the incident radiations of X-rays. X-ray materials are therefore coated on both sides or are abnormally thick. Because of developing and fixing difficulties of a thick emulsion, the former is the more desirable. To increase the photographic action on the sensitized emulsion, it is customary to place the emulsion behind an intensifying screen coated with calcium tungstate which fluoresces under the action of X-rays. The greater part of the exposure is therefore due to visible fluorescent light from the intensifying screen.
Section VII
SAFELIGHTS
Use of safelights.
Paragraph
117
117.	Use of safelights .—Safelights are used in processing photographic materials where it is necessary to view the emulsion during development or to furnish sufficient light for visibility in darkroom
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operations. Essentially, they are filters whose function is to transmit a maximum of visible light to which the emulsion is not sensitive or is only somewhat sensitive. Since color sensitivity varies with different emulsions, the light transmission properties of safelights must vary accordingly.
a.	Noncolor sensitized (ordinary) emulsions of the slower speeds may be safely processed under any safelight not transmitting blue or violet radiations (series 00, 0, or 0A). Such safelights are usually yellow or yellow-green in color. The faster ordinary emulsions have an extended sensitivity and should be processed under a red light (series 1).
b.	Orthochromatic emulsions should be processed under a deep red light (series 2) since their sensitivity range does not include red.
c.	Orthopanchromatic emulsions and those panchromatic emulsions sensitized primarily to blue may be processed under a dark green safelight (series 3). Hyperpanchromatic and panchromatic emulsions of great speed should be handled in total darkness.
(I. Infrared emulsions should be handled in total darkness or with the aid of an infrared safelight (series 7). This safelight, although “safe” for use with infrared material, can not be safely used with orthochromatic or panchromatic materials.
e. The results of printing, both contact and projection, are ordinarily judged in the darkroom so that proper safelights are necessary. Chloride papers can be safely processed under yellow light (series 00). but bromide papers should be handled under orange or greenish-yellow light (series 0 or 0A).
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Chapter 5
OPTICS
•	Paragraphs
Section I.	Properties of light_____________________________118-120
II.	Application of light____________________________121-137
Section I
PROPERTIES OF LIGHT
Paragraph
Definition_______________________________________________________________   118
Theory of light____________________________________________________________ 119
Characteristics of	light____________________________________________________120
118. Definition.—Optics has been defined as the science treating of light, its genesis and propagation, the effects which it suffers and produces, and other phenomena closely associated with it. A textbook on the subject usually includes also the control of light by means of prisms, lenses, mirrors, and other media. In this manual, however, only so much of optics will be presented as will achieve such familiarization with the lenses used in photography as will guide the photographer in the selection of the most suitable type of lens for the kind of work in hand.
119. Theory of light.—The generally accepted theory of light is that it is propagated as a wave action or radiation. The speed of light is constant for all radiations in a given medium and is approximately 186,000 miles a second in air. If light enters a denser medium the wave is shortened, but the number of pulsations (waves per unit of time) remain constant. The waves per unit of time are known as the frequency of the vibration. Since the wave is shortened when light transverses a denser medium and the frequency of vibrations remains constant, the speed of the light is lessened. Sunlight is the simultaneous perception of many and varied waves or radiations which produce the sensation of white light. If a beam of sunlight is passed through a glass prism, the colors of some of its component rays are made visible. The most prominent of these are red, orange, yellow, green, blue, and violet, but there are also intermediate shades of colors between each of the six and it has been found that there are waves of colors beyond each end of this visible band or spectrum which cannot be seen with the eye. Those below the red end are known as the infrared rays, and those beyond the violet are called ultraviolet rays. The infrared rays are too long to be seen, and the ultraviolet rays are too short.
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120. Characteristics of light.—Light is capable of being refracted, reflected, transmitted, or absorbed.
a. Refraction.— (1) When a jay of light passes obliquely from one medium into a medium of different density, its direction is changed. This characteristic enables a lens to form an image. A ray of light entering any medium perpendicularly to its surface is called a “normal ray.” Its direction is unchanged. (See fig. 14.)
Refraction
Figure 14.—Refraction of light.
(2) When white light enters a prism, the waves are refracted in different degrees dependent upon the length of the waves. The red rays are refracted the least and the violet rays the greatest. This phenomenon is called “dispersion.” (See fig. 15.)
b. Reflection.—When light is diverted from a surface, the action is called “reflection.” The reflected ray is in the same plane and at the same angle to the surface as the incident ray. (See fig. 16.)
c. Transmission.—Light passing through a medium is transmitted. If objects can be clearly distinguished when viewed through such a medium, the medium is transparent. When objects are not clearly distinguishable when viewed through a medium, it is translucent. When
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Figure 15.—Dispersion of light through a prism.
BASIC PHOTOGRAPHY
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Figure 16.—Reflection of light.
light is transmitted through a translucent material the rays are scattered, producing the effect called “diffusion.” (See fig. 17.)
Figure 17.—Transmission of light.
d. Absorption.—Light which is incident upon a medium and is not reflected or transmitted is absorbed. An opaque substance is one which does not transmit light but which may or may not be capable of reflecting light.
Section II
APPLICATION OF LIGHT
Paragraph
The lens_________________________________________________________________121
Formation of images_______________________________________________________122
Focal length of a	lens----------------------------------------------------123
Use of terms--------------------------------------------------------------124
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Paragraph
Speed of a lens_________________________________________________________125
Circle of confusion_____________________________________________________126
Hyperfocal distance________________________'____________________________127
Depth of field__________________________________________________________128
Depth of focus__________________________________________________________129
Lens definition_________________________________________________________130
Angle of field__________________________________________________________131
Angle of view___________________________________________________________132
Conjugate distances_____________________________________________________133
Resolving power________________________________________________________ 134
Lens aberrations________________________________________________________135
Cleaning a lens_________________________________________________________136
Care of a lens__________________________________________________________137
121.	The lens.—a. Description.—A lens is a transparent medium having two opposite regular surfaces which forms an image by changing the direction of rays of light. Although lenses can be made of any refracting medium, they are usually composed of glass.
ft. Function.—The function of a lens in photography is to project an image of an object. A lens must be designed to refract the light in such a manner that the rays from any one point of the object, irrespective of where they fall upon the lens, will meet, forming an image of the point. The extent to which a lens will refract a ray of light depends upon the curvature of the lens surfaces, the thickness of the lens, and the kind of glass of which it is made.
122.	Formation of images.—a. Every point on an object sends out rays of light in aH directions. These may either originate within the object or be reflected by it. It is the function of the lens to project these rays to a common plane in the form of an image. As the rays from a single point in the object pass through the lens, they are refracted and converge to a single corresponding point in the image. The point at which the rays from the object converge is called the “focus.” Rays from every point on the object are similarly treated, resulting in a collection of points which forms an image in an inverted position. Image formation is illustrated in figure 18.
ft. The plane on which a lens forms an image is known as a “focal plane” and the distance from this plane to the lens depends upon the distance of the lens from the subject and the focal length of the lens. Ordinarily a camera is provided with a mechanical means of adjustment for focusing; that is, moving the lens at different distances from the focal plane depending upon the distance the lens is from the object or subject to be photographed. As aerial cameras are ordinarily used at the lens infinity distance or farther from the subject, they are usually built without a focusing adjustment. Some types of
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© Image of subject.	® Subject.
Figure 18.—Image formation.
hand-held cameras employing lenses of very short focal length do not have a focusing device and are known as “fixed focus.”
123.	Focal length of a lens.—a. When rays of light parallel to the optical axis of a lens are incident upon a positive lens surface, they are refracted by the lens and intersect on the opposite side of the lens at a point called the “focal point.” The distance from this point to the optical center of the lens is the “focal length.” Since a negative lens diverges rays of light, there would be no real intersection of the refracted rays. To find the focal point and focal length of a negative lens, the refracted rays are extended backward until they intersect. The intersection of these virtual lines is the focal point of the negative lens, and the focal length is the distance from it to the optical center of the lens (fig. 19).
Figure 19.—Focal length of lens.
~b. A focal length may be defined also as approximately the distance from the lens to the projected image when the lens is focused on an object at infinity distance for that lens.
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c. I here are three factors which determine the focal length of a lens; namely, the curvature of the lens surfaces, the kind of glass used in its construction, and the separation between the lens elements. The first two factors cannot be changed but the third factor is variable and may be used to change the equivalent focal length. Some lenses are so mounted that the front element can be moved, thereby changing the focal length. Cameras of this type have a fixed distance from the rear element to the focal plane. They are consequently focused on objects by moving the front element. This type of lens is also used in cinematography to produce special effects.
Figure 20.—Size of image in relation to focal length.
d. The size of the image is directly proportional to the focal length of the lens. Io illustrate, suppose it is desired to photograph an object, such as a tree, and that the camera is placed at such a distance from the tree that with a lens of 10 inches in focal length a clearly defined image of the tree 1 inch in length is obtained on the focusing screen. Replacing the 10-inch lens with one having a focal length of 20 inches, a clearly defined image of the same tree would then be 2 inches or twice as long as the image given by the 10-inch lens if the position of the camera remains unchanged (fig. 20).
124.	Use of terms.—In photographic optics, there are a number of technical terms so commonly used that all photographers should
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know them and in their work take advantage of the optical law involved. These common terms are—
a.	Speed of a lens.
b.	Circle of confusion.
c.	Hyperfocal distance.
d.	Depth of field.
e.	Depth of focus.
f.	Lens definition.
g.	Angle of field.
h.	Angle of view.
i.	Conjugate distances.
j.	Resolving power.
k.	Aberrations.
125.	Speed of a lens.—The speed of a lens is determined by two factors: the diameter of the effective aperture which, practically speaking, is the width or diameter of the lens, for obviously through a large aperture more light will pass than through a smaller one; by the bellows extension, which is the distance the light has to travel after passing through the aperture until it reaches the film.
a.	f/ system,.—This speed is usually expressed in terms of the ratio existing between the diameter of the effective aperture and the focal length, that is, focal length divided by diameter. This is the basis of what is known as the // system used in marking diaphragm openings. This ration of // value may be determined from the following formula:
f/=F+D
in which // represents the speed of the lens, F the focal length, and D the diameter of the aperture or opening. For example, if the diameter is 2 inches and the focal length 8 inches, the speed would be expressed under this system //4. The amount of exposure required at different lens apertures or openings varies directly as the square of the f/ value. If the diaphragm is set at f/4, and the required exposure is 4 seconds, at //8 the required exposure would not be twice as much, or 8 seconds, but 16 seconds. The formula for readily computing this is:
//2:/A2::Uh
in which t represents exposure time required at original f/ setting, tr the exposure time required at desired /A setting, and f/r the new diaphragm setting required. If the diameter of the //4 diaphragm setting is 2 inches on a lens having a focal length of 8 inches, then the
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diameter of diaphragm setting //8 would be 1 inch. As shown in figure 21, a square with sides 1 inch in length has an area only one-fourth that of a square with 2-inch sides, so that four times more light would pass through an aperture 2 inches square than through one that is 1 inch square.
Figure 21.—Areas of diaphragm openings.
b.	Effect of bellows extension on lens speed.—When the bellows of a camera are extended to any length greater than the optically fixed focal length of the lens for objects at infinity distance or beyond, the speed of the lens as indicated on the lens barrel or shutter is not the actual speed. Therefore, the speed as engraved on the barrel or elsewhere is the true speed only when the distance from the lens to the image plane is equal to one focal length. When this distance exceeds one focal length, the actual or effective speed is less than the indicated speed.
(1) Inverse square law.—The effective speed of a lens is diminished in proportion to the extension of the camera bellows beyond one focal length because light intensity reduces as the distance the light travels increases. The extent to which light intensity varies with respect to travel is expressed by the inverse square law which is as follows: The intensity of light varies inversely as the square of its distance from the source (fig. 22). The shaded area at point A represents the
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sensitized material, which is a certain distance from the lens. When the film is moved to point which is twice the distance from the lens, the light is so spread out that it covers a surface four times the size of the film. Therefore, the intensity of the light on the film at this point is only one-fourth of what it is at point A. At point C, which is three times the distance, the intensity of the illumination is one-ninth. At point D, four times the distance, the intensity is only one-sixteenth.
Figure 22.—Inverse square law.
(2) Variance.—Photographic exposures vary, not inversely, but directly as the square of the distance from the light source. For example, if the film is 12 inches from the lens and the correct exposure time is 2 seconds, the time necessary if the film is placed 24 inches from the lens will be 8 seconds. The solution is as follows: Original bellows extension squared is to the new bellows extension squared, as the original exposure is to the new exposure.
122: 242:: 2 seconds : x seconds = 8 seconds
126. Circle of confusion.—The circle of confusion is the diameter of the circle to which the image of a point will spread at the focal plane. It is expressed as a numerical valuation and is determined by the manufacturer of the lens. A circle of confusion is obtainable only when the image of a point in the object space is out of focus. The only practical use made of the circle of confusion is in the computation of the hyperfocal distance and the depth of field. The
83
C
D
'B
A
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diameter of the circle is an arbitrary constant, the magnitude of which is dependent upon the enlargement and viewing distance of the final print. For critical definition the circle of confusion in a print to be viewed at the distance for normal perspective should not exceed Vi’ooo °f the focal length of the camera lens.
127. Hyperfocal distance.—The distance from the lens to the nearest plane in sharp focus, when the lens is focused at infinity distance, is called the hyperfocal distance (fig. 23). From the formula which follows, it will be seen that the hyperfocal distance (H. F. D.) increases as the focal length increases, and decreases as a smaller diaphragm setting is used. The H. F. D. of any lens is found by multiplying the focal length squared by the reciprocal of the circle of confusion and dividing by the // value. This result divided by 12 will be the H. F. D. in feet.
(y=xl/c)^(//xl2) or'7*hC = H- F. D.
c represents circle of confusion, F equals the focal length, and //is the diaphragm setting. When a lense is focused at infinity or at the hyperfocal distance it will be found that acceptable focus extends towards the lens to approximately one-half the distance from the lens to the hyperfocal distance. Thus the acceptable depth of field is greater than the distance from the hyperfocal distance to infinity.
Figure 23.—Hyperfocal distance.
128. Depth of field.—a. The depth of field of a lens is the distance from the nearest point of the subject in acceptable focus to the farthest point of the subject in acceptable focus. Depth of field decreases either as the size of the aperture or as the focal length increases. Depth of field increases as the object distance increases. All lenses having the same speed and focal length have the same depth of field. Variation of the factors governing depth of field may be stated as follows:
(1)	With a given focal length and object distance, the smaller the diaphragm opening, the greater the depth.
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(2)	Ata given object distance and diaphragm opening, the shorter the focal length, the greater the depth.
(3)	With a given focal length and diaphragm opening, the greater the object distance up to infinity, the greater the depth.
b.	A formula for determining the depth of field of any lens with the subject at the given distance is as follows:
Let	d= lens to subject distance
II.	F. D.= hyperfocal distance
Dn= distance to nearest plane of focus Df= distance to farthest plane of focus
H.F.D.Xd
F. D. + d H.F.D.Xd
F.D.-d
The distance from the near plane of focus to the far plane of focus is the depth of field.
Df—Dn=depth of field
c.	The portion of the subject which will appear in sharpest focus in the image lies in a plane which is approximately two-fifths of the distance into the depth of field. For this reason it is desirable to adjust the camera with the lens set at its greatest aperture so that the plane of best focus will be two-fifths of the distance into the desired depth of field; then decrease the aperture until the desired depth of field is obtained.
129.	Depth of focus.—Depth of focus is the allowable distance on either side of the focal plane in which acceptable focus is rendered. In practice, depth of focus is used mostly in connection with focusing screens and determines the extent or latitude of allowable movement of the focusing screen within which good focus is rendered.
130.	Lens definition.—Definition is the accuracy with which a lens will render an image. If it is impossible to secure a wire-sharp image with a particular lens, the lens has poor definition.
131.	Angle of field.—a. The angle of field or angular field of a lens is a property of the lens and may be defined as the angle subtended by lines that pass through the center of the lens and locate the diameter of the maximum image area within the specified definition of the lens. (See fig. 24.) It is the function of the particular type of lens to form properly an image within the desired angle. For example, wide angle lenses are made to “cover” wide angles and telephoto lenses a relatively narrow angle.
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Figure 24. -Angle of field of a lens.
b. The covering power of a lens is the area of the focal plane lying within the circle determined by the angle of field. (See fig. 25.)
132.	Angle of view.—The angle of view is considered as the angle subtended by lines which pass through the lens to diametrically opposite corners of the plate or film used. This angle of view of the camera varies with the photographed image and the bellows extension. (See fig. 26.)
133.	Conjugate distances.—For every distance that an object may occupy with respect to a lens there is a corresponding distance for the image. The object and image are conjugate (coupled together) to each other relative to the lens, and the corresponding distances from object and image to lens are called “conjugate distances.” Any point of an image with its corresponding point of the object may be called “conjugate foci.” (See fig. 27.)
134.	Resolving power.—The resolving power of a lens is the optical ability of a lens to record minute lines or points clearly, distinctly, and separately, and is a function of the effective diameter of the lens. The smaller the effective diameter of the lens, the greater the resolving power.
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Figure 25.—Covering power of lens.
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Figure 26.—Angle of view.
135. Lens aberrations.—An aberration is the effect of an optical error and results from the deviation of light from its desired path through the lens to the image. There are seven aberrations which are common to lenses and are generally corrected in high grade photographic lenses. These aberrations are chromatic, curvature of field, spherical, coma, astigmatism, curvilinear distortion, and optical flare. Most high-grade photographic lenses are called “anastigmats” and are corrected for the first six of the named aberrations. Optical flare is present in all lenses since it is caused by reflections from the surfaces of the lens elements, but is somewhat reduced by the use of a suitable lens hood. Some of the latest high-grade photographic lenses are chemically treated on the surfaces exposed to air. This treatment is a recent discovery which greatly reduces optica] flare within the lens. Although an anastigmat is corrected for chromatic aberration, the correction is not perfect since red rays focus a little beyond the focal plane. An apochromatic lens is one which is further
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Ang/e ofP/'e w
/- e/7s	I
/Vaxirnurn
Angle of flew
—P/afe
-Cfrc/e of Light
XF V2' 3'
Figure 27.—Conjugate distances.
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corrected for chromatic aberration and focuses rays of all visible colors on very nearly the same plane. This lens is also corrected for the other common aberrations with the exception of flare. In a lens which is to be used for photographic purposes, these seven major defects must be reduced to the lowest possible values in lens design by proper selection of glasses, lens thicknesses, curvatures of various surfaces, and spacing between the elements.
136. Cleaning a lens.—A lens should be cleaned only when necessary. Lenses in storage in warm humid climates should be cleaned at least every 30 days to prevent the formation of fungus growth. In cleaning a lens, all loose dust should be removed by brushing with a soft camel’s-hair brush. A vacuum system may be used, provided care is exercised to avoid striking the lens. Breathing on a lens and polishing it with a clean soft cloth or paper lens tissue will assist in the removal of the oily film resulting from finger prints, etc. A solvent will not be used unless specified by a Technical Order and designated as such for the purpose.
137. Care of a lens.—A lens should not be subjected to direct sunlight, excessive heat, moisture, injurious acid fumes, nor to the possibility of any physical damage. Prolonged exposure to direct sunlight, heat, or moisture may cause the lens elements to separate and allow air to enter between them. This will cause an adverse refracting of the rays of light, resulting in an inferior image projection. Lenses should be stored in a dry place of moderate temperature, in a suitable container, and preferably capped.
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Chapter 6
FILTERS
Paragraphs
Section I. General______________________________________138-143
II. Nature of color_____________________________144—145
III. Application_________________________________146-151
Section I
GENERAL
Paragraph
Definition________ _______________ ______________________________________138
Composition_____.	____________________________________________________139
Purpose______'___________________________________________________________140
Action___________________________________________________________________141
Factors--------------.___________________________________________________142
Care_____________________________________________________________________143
138. Definition.—A filter is a medium used to regulate the intensity or color of light.
139. Composition.—a. Some filters are made of dyed gelatin which is accurately compounded and the color standardized by comparison with a permanent standard. Gelatin or “wafer” filters may be used as they are or they may be cemented between glass. Some gelatin filters, cemented or not, are susceptible to fading at high temperatures. If uncemented, extreme care should be exercised in handling, as fingerprints and dirt will lower the efficiency of the filter. The chief advantages of gelatin filters are:
(1)	They are available in a wide range of color or transmissions.
(2)	They are easily adaptable under various conditions: they can be cut to any shape; they can be used in front of the lens, behind, or between the lens elements; or if necessary, they can be used in front of the light source in any size because of the low expense in comparison to cemented filters.
(3)	In changing from one filter to another, there is no appreciable change in focus of the image. Focusing may be accomplished with or without the filter because gelatin filters do not shift the plane of the image.
b.	Filters cemented between glass are of two grades, A and A, the letter denoting the optical quality of the glass.
(1)	The best cemented filters are made with A glass which is ground and polished optically flat with both surfaces parallel. Fillers of this type can be used for the most exacting requirements in any type of photographic work.
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(2)	B glass filters are of good quality glass and are suitable for amateur and commercial work. The surfaces of the glass are plane parallel but are not ground optically flat, and are not recommended for use with lenses having focal length greater than 10 inches, especially if large apertures are used with the lens.
c.	Colored glass filters are the most permanent in respect to color transmission but are neither available in such a wide variety as are dyed gelatin nor are they as easy to reproduce as to standardization of transmission. The color of these glass filters is determined by metallic salts which are added to the glass when it is made. Glass filters of this type are practically unaffected by temperature. They are made of A glass quality and therefore of high optical excellence.
d.	Any filters containing glass will move the plane of focus back slightly if they are placed in front of the lens. In many cases, such as landscape photography, this alteration is not important but when sharp images are required, it is necessary to focus with the filter in place.
e.	Quite often a filter does not transmit enough light for accurate focusing. If a cemented filter is to be used, “dummy” filters are placed in the filter position during focusing and replaced by the real filter for the photograph. The refraction of light and consequent “moving back” of the image plane is compensated for by the use of the dummy. A dummy consists of plain glass with no selective absorption but nevertheless alters the image rays in a camera.
140.	Purpose.—The purpose of a filter is to aid the photographic emulsion by the proper modification of light. The effect desired in using a filter is orthochromatic rendition, exaggeration or elimination of specified wave lengths, or exposure modification.
141.	Action.—A filter produces its effect by absorption but it also transmits light (fig. 28). A wave of light freely transmitted by a filter will photograph as gray or white provided the emulsion is sensitive to that wave length. If a wave is more or less fully absorbed, it will photograph as dark or black. The greatest possible contrast in the use of filters is when photographing two colors, one of which is freely transmitted and the other fully absorbed. A filter may only partially absorb a color producing what is known as “retardation.” The color so retarded will then photograph as a shade of gray, the density of which will be dependent upon the absorption property of the filter to the particular color. A filter may also have the property of absorbing light without modifying a particular portion.
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Figure 28.—Filter action.
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142.	Factors.—The employment of a filter results in the absorption of light to which the photographic emulsion is sensitive. The effective illumination is reduced, thereby necessitating an increased exposure. The number of times the exposure must be increased when using the filter as compared with the exposure necessary without the filter is known as the “filter factor.” The filter factor depends on the absorption properties of the filter, the color sensitivity of the photographic emulsion, and the quality of the light source.
143.	Care .—a. Gelatin filters should be kept in suitable envelopes when not in use and always stored in a clean dry place of moderate temperature, as dampness will cause the gelatin to wrinkle or curl. The bare fingers or hands should never be allowed to come in contact with the surface as grease and moisture from the fingers will cause spots and spoil the filter. It is practically impossible to clean a gelatin filter satisfactorily.
b.	If a gelatin filter is to be cut for a particular purpose, it should be placed between two sheets of dean paper to avoid touching either surface with the fingers.
c.	Cemented filters, when not in use, should be kept in suitable containers. They should not be subjected to excessive light, heat, moisture, or to the possibility of any physical damage. Some gelatin filters will fade upon prolonged exposure to high temperature or bright light, the effect of which will change the color absorbing power. Heat or moisture may cause a separation of the glass elements from the gelatin and consequent deterioration of the filtering properties.
d.	Glass filters should be cleaned in a manner similar to that used in the case of lenses. They should never be allowed to become scratched or badly marked with fingerprints. Grease and dirt are best removed by breathing on a filter and then polishing it with a piece of soft, clean linen or lens tissue paper. If necessary, a glass filter may be cleaned by dampening some fine tissue with a weak solution of alcohol and water and applying it to the surface gently. Care must be taken that this solution does not come into contact with the edge of the filter as the material with which the filter is cemented will loosen and allow air to enter between the glass elements. Any gritty material should be removed from the surface by gentle use of a camel’s-hair brush.
Section II
NATURE OF COLOR
Paragraph
Primary colors_____________________________________________ 144
Secondary or complementary colors____________________________145
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144. Primary colors.—a. The range of wave lengths included in white light extends approximately from 400 to 700 millimicrons. A millimicron is a millionth of a millimeter and is the common unit in measurement of wave length. This is the normal extent of vision and may be equally divided into three regions, 400 to 500, 500 to 600, and 600 to 700. If a filter transmitted the first group of wave lengths, its color would primarily be blue. A filter passing wave lengths between 500 and 600 will be green, and a filter passing the last division of wave lengths will be red. From this division of the spectrum, it is evident that white light can be divided into three primary colors, red, green, and blue. (See fig. 29.)
■MIO	SOO	600	700
I	I----------1--------1------
/ BLUE \	SPECTRAL
/	l\	YELLOW
----------7\
/ GREEN	\
y v. .
Lz i 'RE0 '
_______i  --------—L-k----------------NATURAL YELLOW _*
____I__________I_____.___I__________I____
AvO	500	600	700
THE THREE COLOR SENSATIONS of THE eye
Figure 29.—Primary colors.
&. A filter is considered as red because it does not transmit blue and green. Therefore, blue and green will be subtracted from white light entering a primary red filter. A filter which absorbs red and green light appears blue and one which absorbs blue and red would appear green. When any one filter of a primary color is used, the other two primaries appear dark and the transmitted color appears light.
145. Secondary or complementary colors.—A secondary color is a mixture of two primary colors. A filter of a secondary color will transmit two primary colors and absorb the third. For example, yellow’ is a secondary color. A yellow filter will absorb blue light but will transmit green and red. Another secondary color, blue-green, includes the blue and green regions of the spectrum. A blue-green filter transmits the primaries, blue and green, but completely absorbs red. The third secondary color is a blend of blue and red, and
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absorbs the band of green in the middle of the spectrum. This blend of blue and red is known as magenta. The secondary colors are also called complementary. Yellow absorbs blue so it is complementary to blue. Blue-green absorbs red and is complementary to it. Likewise, magenta absorbs green so it is complementary to green. Each of these secondary colors has a definite band of absorption in the spectrum (fig. 30). The absolute degree of absorption of a color depends upon the saturation or color concentration. For example, a saturated yellow will not pass blue, but a less concentrated yellow will transmit some blue.
'J&	IG o
RGB COLOR OF LIGHT
V
SiteSHSiiMMMMHwWI a
___________
U	Mo
C
RGB
COLOR OF LIGHT
Figure 30.—Color absorption bands in spectrum.
Section III
APPLICATION
Paragraph
Photographic reproduction	of	color_____________________________________147
Orthochromatic rendition______________________________________________   148
Color exaggeration and elimination_______________________________________149
Exposure modification___:________________________________________________150
Special filters____________________________________________ _____._______151
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146.	Colored objects.—Color is the visual interpretation of the various waves of visible light. It is caused by the absence of one or more radiations which are the components of white light.
a.	The color of an object is conditioned by the absorption properties of the object itself. The object will reflect all light rays incident upon it which are not absorbed or transmitted. The true color of an object is the color reflected when the object is illuminated with pure sunlight. Any alteration in the quality of the viewing light will cause a change, not in the absorption ability of the object but in the quality of the light reflected. A light ray which is not present in the illuminant cannot be reflected. This fact will cause a change in the color which is reflected. For example, if red is viewed under a red light, it will appear light. If viewed under blue or green light, it appears dark or black because the color of the viewing light is absorbed by the object.
b.	Visual sensitivity to color varies with the particular color. If a series of colored objects reflecting the same amounts of light are compared under diffuse daylight illumination, the yellow object will appear the most brilliant ; green and orange will be less brilliant, but more so than red and blue.
147.	Photographic reproduction of color.—The result produced when photographic emulsions are exposed to a series of colors receiving common illumination varies with the color sensitivity of the emulsion. The greater the sensitivity of the emulsion to a particular color, the greater the density of the negative and the lighter the shade of gray in which the color will be reproduced in the print. The result obtained is also dependent upon the quality of the light source. For example, blue will photograph darker with artificial illumination than when daylight is used because of the deficiency of blue in artificial light. The response of any photographic material to the relative brightness in which colors are rendered with the material and light source may be altered by the application of a filter possessing selective absorption.
148.	Orthochromatic rendition.—The reproduction of color in its true aspect is called “orthochromatic rendition.” In photography, other than color photography, the rendition of color as color is impossible because color is recorded only in varying shades of gray. Therefore, when speaking of orthochromatic rendition in the ordinary photographic sense it is meant that the color brightnesses will be in their relative shades of gray.
a.	In most outdoor photography and in the copying of colored subjects other than line drawings, orthochromatic rendition is the
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aim sought. The filter used is termed an “orthochromatic filter.” A filter of this nature retards only those rays which are unusually actinic. Since with most emulsions the sensitivity is greatest among the shorter rays of the visible spectrum, the absorptive property of an orthochromatic filter is principally to blue and violet. Perhaps the simplest and most outstanding example of using an orthochromatic filter out of doors is photographing a scene with a blue sky. The blue sky normally will photograph light. To photograph the sky darker, filtering is necessary. The greater the corrective property of the filter, the greater the amount of blue in the sky will be absorbed and consequently in the print the sky will appear darker. The orthochromatic filter usually employed for this purpose is yellow.
b.	Many panchromatic emulsions are highly sensitive to red. Since red passes through yellow, the inherent sensitivity of the film to red will cause red to photograph too light in comparison with other colors. This emulsion sensitivity necessitates the use of an orthochromatic filter of some color other than yellow. In using these emulsions, the red or long wavelengths must be retarded as well as the blue or short wavelengths. Green filters are manufactured expressly for the purpose and are of such properties that red and blue are retarded to the extent of permitting only enough exposure to reproduce them satisfactorily in their relative densities.
c.	In aerial photography, the primary purpose of a filter is haze elimination except when photographing for a special purpose such as camouflage detection. In the case of haze elimination, the desired result is orthochromatic rendition and clarity of detail (fig. 31). The actinic property of haze is particularly troublesome in that its action is so fast that the creation of the image formed by the light rays of objects cannot properly be recorded on the emulsion. Haze may be defined as the effect produced by rays of light emitted from tiny dust particles and moisture suspended in the atmosphere, such moisture and dust scattering the light rays. This scattering may be great enough to obscure visibility. It occurs through the entire spectrum, but is more pronounced among the shorter visible rays and the invisible ultraviolet. This fact and the fact that these waves are more actinic than others produce a photographic exposure obscuring the possibility of individual color or detail separation. A foggy effect with an inferior image recording is the result. A filter which will absorb the shorter waves (more actinic) eliminates this effect by preventing these waves from reaching the sensitized material. The particular filter used depends upon the amount of haze
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298620°- 41---
97
Figure 31.—Haze elimination by use of a filter.
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present. It is therefore a process of subtraction or absorption of light rays.
149.	Color exaggeration and elimination.—Filters used to exaggerate or eliminate a color or colors are generally referred to as contrast filters. They are chiefly used in the reproduction of colored line drawings. If it is desired that a colored line be eliminated from a drawing and the line is on a white ground, a filter which will freely pass the color should be used. The filter should either match the color of the line or be of a darker shade. If the colored line is on a black ground, a filter which absorbs the color should be used. It may be necessary to intensify a color as in the case of a blue signature. Without a filter, the blue would photograph too light to the possible extent of losing its legibility. A red or a green filter absorbs blue and therefore one or the other may be used. The usual procedure is to use the red because reproduction is generally done with artificial light which emits a high percentage of red. The result will be a dense black reproduction on a white ground.
a.	To render a color lighter than it would appear with orthochromatic reproduction, a filter which selectively transmits light of the same color must be used; while to render a color darker, it must be photographed with the aid of a filter which absorbs light of that color.
b.	By the use of contrast filters, any color in a subject may be emphasized or obliterated at will. Colored stains may be eliminated from prints, negatives, or lantern slides in reproduction by using a filter the color of the stain. Filters of the proper color may be selected by looking at the stain through the filters available. The selected filter should be one which will entirely, or as nearly as possible, eliminate the stain.
150.	Exposure modification.—a. Neutral density -filter.—An exposure modifying filter is one which regulates the intensity of light transmitted. A neutral density filter merely reduces the amount of light thereby making possible a greater exposure time or its equivalent. It cannot be classed as a color filter inasmuch as a modification of color is not possible.
b. Polarizing filters.—(1) The purpose of a polarizing filter is to reduce, not the general amount of illumination emitted from a subject, but particular reflections from the subject which are so bright they produce an excessive highlight exposure.
(2) When light falls upon a subject, the light reflected has two components known as specular and diffuse. The specular component produces what is known as gloss. It enables one to see the image
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of the light source more or less distinctly, as when looking at a glossy surface. A matte surface reflects almost entirely the diffuse component. The diffuse component is reflected in all directions, hence does not give rise to an appearance of glossiness nor will it reflect an image of the light source. Because of this, only those surfaces which reflect specular light can be used as mirrors. A body viewed from one position may reflect a very diffused light but when viewed from other angles may exhibit a very high percentage of specular reflection. Specular reflection may be so great that proper image registration of the reflecting body is impossible. A polarizing filter is a device which is used primarily to absorb specular reflections. By adjusting the filter the percentage of this absorption can be controlled. About 50 percent of the diffuse component is absorbed at all positions of the polarizing filter. At a certain position all of the specular component is transmitted while at all other positions some of it is absorbed. At still another position all the specular light is more or less completely absorbed, depending upon the efficiency of the filter and the nature of the specular light. If all specular reflections are absorbed harsh contrasting reflections are eliminated. If the filter is so adjusted that all of the specular light is passed, its apparent presence is intensified. This is because the diffuse component remains approximately 50 percent absorbed. The image contrast will therefore be increased. Although subjects may be made to appear unnaturally glossy (lighting contrast increased) by the use of a polarizing filter, this change in contrast is not nearly so pronounced as it may be in the opposite direction.
151. Special filters.—The filters previously discussed are for the purpose of absorption or transmission of visible light. Quite often it is desired to eliminate or make use of those light rays which are not visible to the eye but which may be exceedingly actinic to a photographic emulsion. These are invisible because of their lengths, but often for the same reason, they may prove exceedingly useful or harmful in photography.
a.	Infrared waves have the property of haze penetration to a much greater extent than the long waves of visible light. Therefore, infrared photography is utilized most often where it is desired to eliminate haze and secure sharp definition and contrast on distant objects. Infrared filters, in general, will transmit only the extremely long visible light waves and the infrared waves so that in use photographic exposures will be only to those waves. Photographic emulsions manufactured for this purpose are particularly sensitized to
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the infrared region but are also sensitive to blue, violet, and ultraviolet. Infrared filters will absorb the short wave lengths of light.
b.	Ultraviolet light is invisible but often degrades blue exposure because of its extreme actinic properties which affect all photographic emulsions. For this reason, it is often necessary to absorb ultraviolet light to obtain true color rendition. Plain glass partially absorbs ultraviolet light but when complete absorption is the goal, a special filter is used. A filter of this type is visually colorless but actually is imbued with some chemical which has the property of complete absorption of ultraviolet light. If it is desired to utilize ultraviolet light, a filter is employed which will absorb most of the visible light but will transmit blue, violet, and ultraviolet. The short wave lengths are often useful in producing images of high resolving power.
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Chapter 7
SENSITOMETRY
Paragraphs
Section I. General__________________________________152-154
II.	Sensitometers____________________________ 155-156
III.	Development______________________________157-159
IV.	Density determinations___________________ 160-162
V.	Contrast determinations__________________163-167
VI.	Measurement of sensitivity______________ 168-171
VII.	Application______________________________172-173
Section I
GENERAL
Paragraph
Definition ___________________________________________________ 152
Scope ---------------------------------------------------------153
Purpose ___________________________________________________    154
152.	Definition.—Sensitometry is the quantitive measurement of the response of photographic emulsions to light.
153.	Scope.—Since in the developing out processes the effect of exposure is apparent only after development, quantitive measurements of sensitivity are also measurements of the development effects. Sensitometric investigations involve the means of determining and expressing quantitively—
a.	Speed or emulsion sensitivity.
b.	Degree of development under various conditions of development.
c.	Measurement and expression of contrast and maximum available contrast under known conditions of development.
154.	Purpose.—Sensitometry provides a method whereby the effect of exposure and development on a photographic emulsion may be studied systematically. In this way it is possible to select and control these factors so that the desired final photographic result may be obtained.
Section II
SENSITOMETERS
Paragraph
Photographic exposure________________________________________155
Sensitometric exposure_______________________________________ 156
155.	Photographic exposure.—Measurements of the response of an emulsion to light are based fundamentally on the density produced under given conditions of development by a known exposure. Expo
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sure is measured in terms of the illumination multiplied by the time during which the illumination acts. From this statement the fundamental formula, E=ITis evident, in which E is total exposure, I is illumination and T is exposure time.
156.	Sensitometric exposure.—a. Light source.—For consistent results, a standard light source is selected which closely approaches the type of illumination under which photographs are normally made. Incandescent tungsten light sources are generally used because they are easily controlled. To approximate daylight, a filter is used between the source of light and the emulsion in making the sensitometric exposure. The filter selected has a bluish hue because incandescent tungsten light predominates in the longer wavelengths which must be subdued. For highest precision, a liquid filter is most satisfactory, but practically, a gelatin filter of the proper transmission will suffice. The light source is operated at a constant voltage and amperage to maintain constant intensity and spectral distribution.
b. Sensitometers.—A sensitometer is an instrument by which a series of progressive exposures is obtained on a photographic emulsion. Since exposure is defined as the product of intensity and time, one of these two factors is kept constant while the other varies. The exposures are made in a series of steps which are evident after development as increasing densities (fig. 32). Sensitometers are of two general types, the time scale and the intensity scale.
Figure 32.—Sensitometric strip.
(1) If time is the variable factor of the exposure, the sensitometer is of the time scale type. A common method of obtaining step exposures on a time scale is to introduce a revolving cylinder in front of the film position. This cylinder has on its surface a series of open slits whose lengths vary in accordance with the exposure times desired (fig. 33). Usually the lengths of the slits increase logarithmically by consecutive powers, or roots, of 2. The most common time factor is the square root of 2; thus each step receives 1.414 times the exposure of the preceding step. Light is directed from the source toward a mirror within the cylinder and is reflected onto the film, thus causing the exposure.
(2) An intensity scale sensitometer utilizes a screen which is placed in front of the emulsion. This screen is of increasing absorbing power
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from one end to the other, and may be either of two types; an optical wedge in which the light absorption is continuous due to gradient density, or a step wedge in which the increase is discontinuous in steps of geometric proportion with a power, or root, of 2 factors (fig. 34). This screen thus varies the intensity of light incident upon the emulsion while the exposure time remains constant.
DEVELOPMENT
Paragraph
General--------------------------------------------------------------      157
Conditions---------------------------------------------------------------  158
Sensitometric	strips----------------------------------------------------  159
157. General.—The effect of exposure is apparent only after development, therefore the conditions of development must be standardized to secure accurate and reproducible results. In establishing standards for developers and development conditions, consideration must be given to the purpose for which the sensitometric work is being done. Since the characteristics of an emulsion can be considerably modified by the constituents of a developer, it becomes evident that if information is to be obtained for practical purposes, the standards adopted must be consistent with those of practical photography.
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Figure 34.—Intensity scale sensitometer.
Section III
Figure 33.—Time scale sensitometer.
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158.	Conditions.—a. The technique of development employed in sensitometry is similar to that required in all photography. It differs in that more attention must be paid to such important factors as uniformity of development, temperature of development, agitation of developing solutions, and prevention of marks, abrasions, streaks, or stains.
ft. Since the sensitometric procedures should be consistent with photographic practice and should also be reproducible, it is necessary to maintain normal conditions of development. Constant and vigorous agitation of the developer is essential to uniform and reproducible development. Solutions must be accurately made for consistent results. Temperatures of solutions must be kept constant and conform with those of normal working conditions.
159.	Sensitometric strips.—To measure accurately the sensitivity of an emulsion, it is necessary to expose several strips of film in the sensitometer. These strips are then developed under specified and controlled conditions for different lengths of time. The developing times vary according to the emulsion and the developer, but generally the range of development time includes under development, normal development, and over development. The difference in development time will produce a difference in contrast. When development has progressed to a certain stage, dependent upon the emulsion, the developer, and other factors, contrast no longer increases with additional development time. When this point is reached, maximum available contrast has been achieved for the emulsion in the developer being used.
Section IV
DENSITY DETERMINATIONS
Paragraph
Density______________________________________________________________160
Measurement of density_____________________________________________  161
Density exposure relation____________________________________________162
160.	Density.—In development the exposed silver halide crystals are changed into grains of metallic silver. The degree of concentration and the magnitude of the silver deposit in the emulsion is expressed as “density.” If a great many particles of silver are present, and do not allow much light to pass through the portion of the emulsion containing them, this portion will be very dense. Density, then, may be expressed in terms of the amount of light transmitted, or in the case of photographs on paper, the amount reflected.
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a.	A photograph of a subject contains highlights and shadows similar to those of the subject. In the negative, the highlights are represented by the heavy deposits of silver or the greater densities. The shadows, which represent the areas of least exposure, are the low densities or small silver deposits. These differences in density are apparent visually and may be expressed as low or high densities. Halftones are the intermediate densities between highlights and shadows.
b.	In sensitometry, density is expressed as a definite valuation; therefore mere visual inspection of a silver deposit in a photographic image is unsatisfactory. For quantitative measurement of sensitivity, the magnitude of a silver deposit is determined optically by the amount of light which is transmitted or reflected. Density is expressed in terms of the light incident upon a negative and the light transmitted through the negative. The ratio of incident light to transmitted light is termed “opacity” and is the expression of the amount of light absorbed. Transmission is the ratio of transmitted light to incident light. Density is the logarithm to base 10 of the opacity, or the logarithm of the reciprocal of the transmission.
D=\og 0=log 2s
The conversion of density values to transmission values is simple. A density of 0.3 for example represents a transmission of y2 01' 50 percent. A density of 0.6 has twice the opacity of a density of 0.3 and its transmission is 14 or 25 percent. Figure 35 gives transmission values for a range of densities.
Density		0. 15	0. 3	0. 45	0. 6	0. 9	1. 0	2. 0	3. 0
Transmission (percent).	70	50	36	25	12.5	10	1	0. 1
Figure 35.
The transmission value given is the percentage of incident light which is transmitted by a given density. From any density value, the transmission can be computed by finding the antilogarithm of the density value. This antilog can be found in a logarithm table and is the opacity value, of which the transmission is the reciprocal. The following problem shows the procedure for computing transmission from density value:
density=.75 antilog .75 = 5.656 = opacity
1*1 1
T— 656— 177=17.7 percent
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For complete understanding of density (exposure relations), a working knowledge of logarithms is essential but for manipulation of density values and subsequent computations, a knowledge of the use of logarithmic tables is sufficient.
161. Measurement of density.—a. The instrument used for the measurement of density values is called a “densitometer.” There are many kinds of densitometers, but the principle involved is the same in each. The fundamental features of any densitometer are a source of light to provide the measuring beam which passes through the negative, a means of limiting this beam to the desired area of the negative, and a means of comparing the brightness of this beam with that of another from the same source which does not pass through any portion of the negative. In this way, a direct comparison is accomplished between the incident beam of light and the beam which passes through the desired area of the negative. A common method of comparison is to adjust the beam which does not pass through the negative until it is equal in intensity to the transmitted beam. The means of varying this beam which does not pass through the negative is calibrated to read density values. The density of a certain area can be read directly from this scale when the incident and transmitted beams are balanced.
b. Figure 36 contains a diagram illustrating a common principle of densitometry. It will be noted that the negative is placed on the stage I. Light from the source A is split into two beams, one passing directly through the negative to the eyepiece J, and the other beam traveling from the lamp to the mirrors B, D, and E. where it is reflected onto a split mirror F. It is reflected from this mirror to the eyepiece where a split field is observed. The wedge W contains an area C of gradient density. By rotation of the wedge, areas of different density can be interposed in the beam from the mirrors, thus changing its intensity. The split field in the eyepiece is balanced by rotating the wedge until the field of the beam which passes through the negative has been equaled in intensity by the proper variation of the intensity of the beam from the mirrors. The reading of density of the desired area in the negative is obtained from a calibrated scale on the edge of the gradient wedge.
162. Density exposure relation.—The relation between exposure and the photographic response of a material is usually presented in the form of a graphic curve in which density is plotted against the logarithm of the exposure. The exposure is generally expressed in terms of the illumination on the exposure plane of the sensitometer, as measured in meter candles, and the time of the exposure on any
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individual step in the strip. The resulting units of exposure are meter candle seconds. Graphically, each individual density is plotted against the corresponding exposure which produced it. A typical resultant curve is shown in figure 37.
uj	^4.
O
LOG E
Figure 37.—H and D curve.
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Figure 36.—Gradient wedge densitometer.
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a.	This method of expressing sensitometric data was developed by Hurter and Driffield and is frequently called the H and D curve, the characteristic curve, or the Z>-log E curve.
b.	For the greater part of its length, this curve is a straight line. Throughout the straight line region, the logarithm of the exposure is proportional to the density produced. Since density is the logarithm of the opacity, it is evident that the opacity is proportional to the exposure within the straight line portion of the curve. The straight line then represents the region of correct exposure. Within this range, density increases proportionally with the logarithm of exposure of the logarithm of subject brightness.
c.	The lower portion of the curve is called the “toe,” and is concave to the exposure axis. There is no definite relationship between the exposure and density in this portion of the curve. The toe of the curve is widely used in making negatives, and is often referred to as the region of underexposure.
d.	The upper portion of the curve, which is convex to the exposure axis, is called the “shoulder.” The increase in density, with exposure difference, decreases steadily as exposure increases, finally becoming zero. This portion of the curve represents the region of overexposure.
e.	Beyond the point where zero is reached, an increase in exposure will produce a decrease in density so that a positive would result instead of a negative. This is called the “period of reversal.” This period would be the result of abnormal overexposure and has no practical value.
Section V
CONTRAST DETERMINATIONS
Paragraph
Effect of development______________________________________________   163
Determination of gamma____________________________,________ __________164
Time-gamma curves___________________________________________________  16J
Development latitude_______________________________________________   166
Gamma infinity________________________________________________________167
163. Effect of development.—An increase in the development time under given conditions of development will produce an increase in density, the increase being greater for the higher densities than the lower densities. This means, that for a given exposure increment, the density differences are increased. As the density difference increases, the angle between the straight line and the log exposure axis also increases. Since this increase in the angle represents a difference in contrast between densities, it is therefore a measure of the degree of development, and variation in contrast by development
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may be expressed in terms of the measure of this angle. Generally it is expressed as gamma and is the tangent of the angle, or the ratio between the difference of any two densities on the straight line and the difference in logarithms of the corresponding exposures.
a.	When gamma is equal to 1.0, the density differences are equal to the differences in logarithms of the exposures on the straight line portion. In a photograph, these exposures are the direct result of brightness differences in the subject; therefore, with development to gamma 1.0, the differences in density are proportional to the logarithm of the brightnesses of the corresponding parts of the subject. The ratio of opacities then, since density is the logarithm of opacity, is the same as that of the representative brightnesses. With development to gamma less than 1.0, the opacity difference is less than brightness difference in the subject. When gamma is greater than 1.0, the opacity difference is greater than subject brightness differences.
b.	The opacity differences determine the contrast of the negatives, therefore gamma is proportional to contrast when the maximum and minimum densities of the negative lie on the straight line portion of the curve. If some portions of the subject are represented by densities which are not on the straight line, then gamma does not represent the true contrast of the negative.
164. Determination of gamma.—a. The value of gamma may be determined by use of the formula:
Gamma (y) = .-——gr v' log E\ - log E,
Draw two perpendicular lines from the exposure axis to their points of intersection on the straight line portion of the curve. Determine the densities at the points of intersection and substitute both density and log E values in the formula. The value of gamma may be found in this manner for any H and D curve (fig. 38).
b. In practice, a transparent scale called a “gammeter” is used to determine gamma. Figure 39 shows one form of gammeter commonly used in sensitometry. In use, the arrow is placed on a point along the straight line of the curve. The base of the gammeter is placed on a line paralled to the log E axis. The vertical axis of the gammeter will then be intersected by the straight line portion of the curve. At this intersection the gamma for the H and D curve is read from the calibrated scale.
165. Time-gamma curves.—Among other factors, gamma is a function of developing time and increases proportionally. If a series of sensitometric strips are developed under equal conditions for
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Figure 38.—Calculation of gamma.
-4.0
-3.8
-3.6
-3.4
-32
-3.0
-2.8
-2.6
-	2.4
-2.2
-	2.0
-1.8
-	1.6
-	1.4
-	1.2
-	1.0
-0.8
-0.6
-0.4
-0.2
-	2 .0 - 1.9 - 1.8 - 1.7 - 1 6 - 1.5
-	1.4 - 1.3 - 1.2 - 1.1 -10 - 0.9 - 0.8 - 0.7 - 0.6 -0.5 - 0.4 - 0.3 — 0.2 -0.1
Figure 40.—Group of H and D curves showing gamma increase.
Figure 39.—A type of gammeter.
different times and the resulting densities of each strip plotted, the result will be a group of II and D curves of increasing gamma (fig. 40). If the values of gamma are plotted on another graph against developing times, the curve will show the relation between development time and gamma for the emulsion in use. This curve is called a time-gamma curve” and from it can be determined the developing time necessary to produce any desired gamma for a specific material in the developer being used. Conversely, gamma can be read from the curve for a given developing time. (See fig. 41.)
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2		
3		
< 0
TIME OF DEVELOPMENT
Figure 41.—Time-gamma curve.
166.	Development latitude.—a. Occasionally it is not necessary to obtain an absolute gamma but certain tolerance may be allowed. Processing must be kept within limits and developing time must not exceed a given time or fall below a corresponding minimum. This range of developing time to produce a given tolerance in gamma is termed “development latitude.”
b. Development latitude may be determined from a time-gamma curve when the tolerance in gamma is specified (fig. 42). It is a very important characteristic when sensitive materials must be developed to specified gamma as in the processing of motion-picture sound records.
167.	Gamma infinity.—Contrast, or the value of gamma, increases with development time. This reaction is definite; that is, a certain point is reached, with prolonged development, where contrast no longer increases. Due to the addition of development fog, the value of gamma decreases beyond the point of maximum contrast. The reason is that the heavy densities have reached a maximum and further development builds up the densities of the lesser exposed areas thereby lowering contrast. This maximum available contrast is termed “gamma infinity.”
a.	The value of gamma infinity depends chiefly upon the sensitized material but varies to some extent with different developing agents.
b.	Gamma infinity may be determined experimentally but since very
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8	______
<■
<	X i '
O	y<	I I
I I I I ________1	I_______1_______I______I_______I__
DEVELOPMENT LATITUDE
Figure 42.—Development latitude.
high densities are involved which may be fog due to long development, the process is subject to experimental errors. Gamma infinity is generally determined by calculation from lower values of gamma. Calculation of gamma infinity involves the use of two sensitometric strips, one of which is developed twice as long as the other. All other conditions of development are the same for both strips. For safety, the longer time of development is usually made short enough to avoid reaching gamma infinity in development. The following formula is used in computing gamma infinity:
7 is the symbol of gamma
y2 is reached in twice the time necessary to obtain yt.
Section VI
MEASUREMENT OF SENSITIVITY
Paragraph
Emulsion speed_____________________________________________________________
Speed determinations_______________________________________________________169
Latitude_______________________________________________________________________
Spectral sensitivity_______________________________________________________171
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168. Emulsion speed.—Several methods of expressing emulsion speed exist and are widely used in photography. Absolute values of film speed have little significance since true speed or sensitivity depends largely upon processing conditions. Relative speeds have definite practical value since they present a direct method of comparing emulsions. By different methods, an arbitrary number to designate speed is assigned to each kind of emulsion. This number serves as an index to the relative speed of the emulsion. In each system, the number increases with the sensitivity, but the different systems are inconsistent and do not always produce results which are comparable with one another because different criteria are used in determining speeds in the various systems.
169. Speed determinations.—The most widely used systems of determining sensitivity of emulsions are based on four principles as follows:
a. Threshold speed.— (1) This method of determining speed is based upon the exposure necessary to produce the least perceptible density (fig. 43). A fast emulsion is one which will produce a perceptible density with relatively low exposure, and conversely, a slower emulsion will require more exposure to produce an equal perceptible density.
Figure 43.—Threshold speed.
(2) The most familiar speed rating based upon threshold speed is the Schemer rating. Since there is no fixed relationship between threshold exposure and that required for satisfactory rendering of the gradations of the subject, the threshold exposure method is inadequate for measuring the effective speed of an emulsion.
b. TL and D speed.—When the straight line portion of an II and D curve is extended to intercept the log E axis, an exposure is indicated which is termed the inertia (fig. 44). The reciprocal of the inertia indicates the speed of the material. This value is often less than
298620°—41----8
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unity so that it is customary to multiply it by some constant to obtain a convenient system of numbers. The number selected as the factor in the American system of H and D speed is 10.
Figure 44.—H and D speed.
(1) If a developer contains bromide or the emulsion contains free bromides, the value of inertia varies with the degree of development. The intersection of the extended straight line of the characteristic curve with the log E axis shifts to the left as gamma increases. Thus the effective speed of an emulsion increases as development is prolonged. For each time of development there is a corresponding II and D speed.
(2) H and D speeds are indicated by numerical values which are directly proportional to sensitivity. For example, an emulsion rated as 1,300 II and D is twice as fast as one rated at 650 II and D.
c. Weston speed ratings.— (1) General.—A modification of the inertia speed rating {II and Z>) is the Weston method by which inertia and the latitude of the emulsion are considered. In this system, the speed is determined from the 7?-log E characteristic of the film which is processed to the value of gamma most often encountered in practice for that particular emulsion.
(2) Method of computation (fig. 45).—Emulsion speed is inversely proportional to the exposure required to produce a given density. The following formula is used to compute Weston speeds:
Where W=Weston speed number en = exposure required to produce a density of 1.0 X gamma
The density is multiplied by gamma to avoid any discrepancy in speed arising from slight variations in gamma and speed is then specified for that gamma. Miniature camera film is usually devel
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oped to gamma = 0.8. Most other types of film are developed to gamma=1.0, or the gamma which reproduces subject brightness. In measurement of speed by the Weston system, the exposure necessary to produce the given density is determined from the ZMog E curve of the desired gamma. Exposure in sensitometry is measured in meter candle seconds which is the exposure unit indicated on the D-log E curve.
—------—---------1
En
Figure 45.—Weston speed.
(«) If a particular film attained the specified density with an exposure of 0.125 meter candle second (M. C. S.), the calculation of the speed rating would be obvious from substitution in the formula, or tjz 4	4	_
H k ~ 225 — 32 and the film has a 'Weston speed rating of 32.
(b) The light source in the sensitometer simulates daylight in its quality when the emulsion speed is to be determined for daylight. If the speed is to be measured for any other lighting, the quality of this light must likewise be simulated in the sensitometer.
d. Minimum useful gradient.— (1) In practice, the speed of a photographic emulsion is determined by the exposure necessary to reproduce the differences in brightness in the shadow portions of the subject. The speed, then, is determined by the exposure necessary to produce a suitable difference in density and not that required to produce any particular density. Differences in density determine the slope, or gradient, of the Z>-log E curve. The maximum gradient is attained in the straight line portion of the curve, and throughout this region the gradient is constant. There is no fixed gradient within the toe of the curve and the gradient decreases as the densities decrease. The point on the toe of the curve where the density difference is just sufficient to produce acceptable tone reproduction in the print is known as the minimum useful gradient.
(2) A common method of determining speeds by this principle
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involves drawing the characteristic curve and selecting the exposure at which the gradient of the curve is 0.3 that of the average gradient for a log exposure range of 1.5. The origin of this exposure range is taken at the speed index point. (See fig. 46.)
I ------LOG EXP. RANGE 1.5
£	zZ
2	//
UJ	//
°	z Z
/	^MINIMUM
GRADIENT
		BASE DENSITY ..............  >-♦	I-------1--—-------------
LOG EXP.
Figure 46.	—Minimum useful gradient.
170.	Latitude.—a. The scale of tones which can be reproduced by a film is known as the exposure range or exposure latitude. This range is indicated on a characteristic curve as the exposure interval between a point fairly low on the toe and another point located on the shoulder (fig. 47). As the brightness range in most scenes is considerably less than this exposure range, wide latitude is given in the choice of camera exposures. The latitude, or exposure scale, of a photographic emulsion is the range of exposures for which there is adequate density gradient for the desired result. While latitude is often associated with the straight line portion of the characteristic curve, normally a greater portion of the curve is used than the straight line.
Z>. Latitude is a very important characteristic of a sensitive emulsion because it indicates the range of brightnesses in a subject which can be satisfactorily recorded in a negative. The latitude of most negative materials is generally much greater than the range of brightnesses in a majority of subjects. The normal range of sub
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ject brightness is about 1-30 and only in exceptional cases does it exceed 1-100. Average latitude of negative materials is approximately 1-200, but is frequently considerably greater. The greater the latitude of an emulsion, the greater is the tolerance in exposure of the subject to produce an acceptable negative. For any given material,’ the greater the range of brightnesses in the subject, the less the tolerance in exposure. The selection of an emulsion to photograph a particular subject is greatly influenced by its latitude.
^—2
i t----L,------t
l>	l2----J
Figure 47.	—Exposure latitude.
171.	Spectral sensitivity.—The variation in the response of a photographic material with the wave length of the radiation to which it is exposed constitutes what is known as “spectral sensitivity,” or as frequently termed “color sensitivity.” The rendition of colors of a subject depends upon the spectral sensitivity of the emulsion in use. The measurement of spectral sensitivity involves the isolation of separate regions of the spectrum and determination of the response of an emulsion to the radiations within these regions.
Section VII
APPLICATION
Paragraph
General __________________________________________________________________ 172
Practical_________________________________________ ______________________173
172.	General.—The principles and results of sensitometric determinations are employed in all branches of photography, but actual measurement of sensitivity is more or less limited to technical and scientific aspects. These determinations are used principally as controls in the production of accurate and consistent results. Every photograph is made under conditions which are determined in
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sensitometric work. The photographer selects an emulsion for a particular job, not haphazardly, but for definite reasons. If the subject has a great brightness range, he selects a film which has sufficient exposure latitude as determined for him by sensitometry. The speed of the emulsion regulates the exposure and an emulsion of suitable speed is selected for the subject. The particular type of lighting in use governs the selection of a material with appropriate color sensitivity. When the exposure is complete, the emulsion must be processed. Sensitometry again tells the photographer what developer to use for the particular emulsion to obtain proper tone gradation in the negative. He must know the degree of development necessary to reproduce the contrast of the subject as determined by the time, temperature, and condition of the developer. After the negative is finished, the next phase in the production of the photograph is to produce the positive. If the positive is on paper, the photographer must know what paper to use regarding contrast and tone and the conditions of development. It is unnecessary for any photographer to understand perfectly how all sensitometric measurements are made, but a complete understanding of the principles involved is an undeniable aid in the production of superior photographs. Proper selection of materials for particular or general work undoubtedly is the result of sensitometric principles. Fundamentally, similar problems confront every photographer in every branch of photography, so that sensitometry applies every time a photograph is made.
173.	Practical.—Sensitometry is applied extensively in several branches of technical photography. Among these are the motionpicture industry, color photography, and the manufacture of sensitized materials.
a.	Motion pictures.—(1) In the processing of motion-picture film, sensitometric methods of developer testing and control are employed exclusively. To insure the desired result in the projected image, it is essential that the materials are developed to a definite gamma. This can only be attained when the degree of development can be controlled, and is especially true in the case of processing sound track which is very susceptible to any change of development contrast.
(2)	The time of development necessary to produce the desired gamma is determined by developing several sensitometric strips. These strips are developed to different times and the degree of development or gamma of each strip ascertained from the time-gamma curve which in turn establishes the time of development necessary to attain the specified gamma. If the desired gamma is not reached within a specified time, the developer is not sufficiently active and
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replenisher must be added to bring the developer up to a standard condition or new developer made. In large scale production, tests are usually made at half-hour intervals.
b.	Color photography.—(1) An example of the use of sensitometry in color photography is the production of separation negatives for color printing. These negatives are made with different filters and consequently must be developed differently to obtain equivalent results since development contrast varies with the color of light to which an emulsion is exposed. The determination of the degree of development of these individual negatives would be impossible by any other method than sensitometry. The filter factors for the particular emulsion must be accurately known to expose properly the negatives. These factors are easily and accurately determined by sensitometric means whereas any other method would be lengthy and inaccurate.
(2) Another application to color photography is the processing of Kodachrome film. While this processing is not influenced by the photographer, the importance of sensitometry is still evident. Kodachrome processing is rather complicated and delicate, and necessitates careful control. Sensitometric strips on Kodachrome are read by means of a color densitometer which has three gradient wedges of red, green, and blue, the primary colors. Three H and D curves are plotted for each strip. If the three coincide in the straight line portions, the color balance is that of a neutral gray. If the curve for any color varies from this coincidence in relation to the other two, it is evidenced by a sideward shift and the processing can be adjusted accordingly to obtain correct color balance.
c.	Emulsions.—The most important application of sensitometry is in the manufacture of emulsions. Since the ordinary photographer seldom has facilities for making accurate sensitometric determinations, the manufacturer must do it. Every emulsion manufactured for professional and amateur photography is thoroughly tested. Complete recommendations are issued concerning all films, plates, or papers so that any photographer can intelligently use and process any emulsion. Understanding of sensitometric principles is invaluable to every photographer in his selection of a proper emulsion to fit a particular or general need and for intelligent and accurate processing. The photographer who makes superior photographs consistently, undoubtedly has a working knowledge of sensitometric principles.
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Chapter 8
GROUND CAMERA PHOTOGRAPHY
Paragraphs
Section I. General__________________________________ 174-176
II.	View camera_______________________________177-180
III.	Hand camera_______________________________181-187
IV.	Composition_______________________________188-190
V.	Exterior subjects_________________________191-192
VI.	Interior subjects_________________________193-199
VII.	Identification photographs_______________ 200-205
VIII.	Photography of moving objects____________ 206-211
IX.	Flashlight photography____________________212-218
X.	Exposure--------------------------------- 219-225
Section I
GENERAL
Paragraph
Scope__________________________________________________________________174
Purpose----------------------------------------------------------------175
Types of	cameras______________________________________________________176
174.	Scope .—Ground camera photography embraces the making of any negative with a ground camera and its allied equipment.
175.	Purpose.—Ground camera photography includes the making of photographs for the purpose of military intelligence, historical record, and technical information. It includes the photographing of airplanes or parts thereof, equipment, machine parts, construction work, buildings, military activities, personnel, etc. The cameraman will use the type of ground camera best suited for the purpose.
176.	Types of cameras.—Ground cameras may be divided into three classes as follows:
a.	View cameras.—View cameras are portable cameras generally used on a stand or tripod and have adjustments permitting restitution.
b.	Rand cameras.—Small portable cameras that are held by the operator are hand cameras. They produce a smaller size image than the average view camera and since they are held in the hand, they can be used under conditions impractical with a view camera.
c.	Copying cameras.—Cameras designed especially for photographic reproduction are copying cameras. Although usually portable, they are generally cumbersome and therefore not easily transported. Their use differs so much from that of the view and hand-held type cameras that a special chapter on copying (ch. 11) is included in this manual.
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Section II
VIEW CAMERA
Paragraph
Setting up camera___________________________________________________________177
Use of the sliding block___________________________________________________ 178
Movable lens board__________________________________________________________179
Use of vertical tilt and horizontal swing________________;______.___________ 180
177.	Setting up camera.—To use a view camera it should be secured to a tripod. For subjects such as landscapes, buildings, machines, and the like, the camera should be leveled. For special effects and some types of “close-up” work the camera may be placed at any desired angle. When so used special precautions must be taken to insure the rigidity of the camera and tripod.
178.	Use of the sliding block.—The sliding block is a device to which the camera must be secured. It is adjustable to different positions on the camera track. When photographing close-up subjects at an acute upward or downward angle the sliding block may be used to change the position of the camera on the track, thus altering the scale of the photograph. It may also be used to balance the camera when a long bellows extension is used. It will also permit the location of the lens directly over the center of the tripod screw, facilitating panoramic exposures which overlap at a point of uniform scale by allowing the turning of the camera with the lens remaining on a common axis.
179.	Movable lens board.—The lens board of a view camera should be provided with a mechanism which will raise and lower the position of the lens and also move it in a lateral direction. This feature is used for properly placing the image of the subject on the ground glass. The lens should not be shifted so far in any one direction that the image on the focusing screen will fall outside the accepted angle of illumination.
180.	Use of vertical tilt and horizontal swing.—View cameras are equipped with a vertical tilt and horizontal swing. The vertical tilt is a device by which the ground glass can be tilted forward or backward on a horizontal axis. The horizontal swing is a device by which the ground glass can be swung forward or backward in a horizontal direction on a vertical axis. These devices are used for two distinct purposes; improvement of focus and restitution of the image. When either the vertical tilt or horizontal swing is used to improve the focus, the perspective is changed from the normal. Likewise, when used to improve perspective, certain parts of the subject will be thrown out of focus.
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a.	If a camera on the ground is focused at about midway to the top of a tall building, an inspection of the image on the ground glass will disclose the following:
(1)	The image of the building is inverted on the ground glass.
(2)	Both the lower part and top of the building are slightly out of focus.
(3)	The .vertical lines of the building converge toward the top.
b.	The lower part of the building is out of focus because it is nearest the lens and will focus in a plane farther from the lens than the vertical plane of the ground glass. The top of the building is out of focus because it is farthest from the lens and will be in focus in a plane nearer the lens than the plane of the ground glass. If the vertical tilt of the camera is adjusted so that the bottom part of the ground glass is moved toward the lens and the upper part is moved away from the lens, the upper and lower parts of the image will approach sharp focus. An inspection of the image will reveal that while the focus is improved, the vertical lines of the building are more convergent than they were when the ground glass was in its original vertical position. If, on the other hand, the vertical tilt of the camera is tilted so that the top part of the ground glass is nearer the lens, the ground glass will be in a plane more nearly parallel to the vertical plane of the building and the vertical lines of the image will correspond more closely to the vertical lines of the building. (See fig. 48.) It will also be observed that the extremities of the image are not in sharp focus. As a rule, the lens aperture can be reduced sufficiently to bring these parts into sharp focus. If not, the distance from the camera to the building must be increased. If this distance cannot be increased, it is better to compromise the adjustment than to have any part of the image out of focus. If a camera is pointed downward on a subject, the same difficulties will be encountered but perspective will be exaggerated in the opposite direction.
c.	In photographing a horizontal subject with the camera near one end, the effect will be the same but in a horizontal direction. In this case, the horizontal swing is used to remedy the difficulty.
d.	There are occasions when the vertical tilt or horizontal swing must be used to secure sufficient depth of field with a sacrifice of good perspective. Often these camera adjustments are used to correct perspective at the expense of securing sharp focus, but generally it is possible to stop down the lens sufficiently to secure both good perspective and sharp focus.
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Figure 48.—View camera adjustments.
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e.	Some cameras are equipped with attachments which permit the lens to be tilted on both a vertical and horizontal axis. These adjustments are used for the same purposes as the -vertical tilt and horizontal swing, but primarily for the correction of focus. They are also used in conjunction with this tilt and swing to give a greater range of adjustments for corrections. A camera that is additionally equipped with a tilting bed may be tilted upward or downward, permitting a better control of perspective through the proper manipulation of the “swings.” Vertical lines can be made to remain vertical and parallel horizontal lines made to converge slowly or not at all. Thus a great depth of field is possible with the lens at full aperture, permitting exposures to be made at larger apertures with greatly improved accuracy of focus.
Section III
HAND CAMERA
Paragraph
General____________________________________________________________________181
Adjustments________________________________________________________________182
Accessories____________________ _________________________—_________________183
Vernier focusing scale_____________________________________________________184
Built-in shutter lock________________________—___________ _________________185
Reflex type----------------------------------------------------------------186
Range finders________________ _ ___________________________________________ 187
181.	General.—This type of camera is designed for general utility and will accommodate roll film, cut film, and film packs. These cameras are often fitted with both focal plane and between-the-lens shutters. When equipped with a lens-coupled range finder and synchronous photoflash, such cameras are useful for news, sport and informal group photography. The synchronized flash is often used as a supplement to daylight to illuminate shadows, in weak daylight, or at night when there is insufficient light for exposures. Being fitted with well-corrected anastigmat lenses from //4.5 to //2.8 maximum working aperture and having focal lengths from 3^ to 6% inches, these cameras can be used frequently to obtain photographs that would be impossible with a view camera making 8- by 10-inch negatives and using a lens of 12 inches focal length.
182.	Adjustments.—Focusing is accomplished for infinity by drawing the camera front outward until it reaches the infinity stops that are bolted to the bed track. These stops should not be moved from their set position. For distances less than infinity, the camera front is moved forward with the bed track by a rack and pinion device.
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183
183. Accessories.—In addition to the synchronized range finder, the graphic type of hand camera is fitted with two view finders, the peep sight and the parallax. The peep sight (fig. 49) has two parts, one attached to the rear of the camera body and the other a wire frame attached to the camera front. If the wire frame and the rear sight are raised and the eye brought close to the rear sight, all that can be seen in the wire frame will be included in the picture. This type of view finder is very useful when making action photographs. The parallax view finder is a tubular device mounted at the top right side of the camera body. It has adjustment for parallax and provision in the front, which is removable, for accepting interchangeable masks for use with lenses of different focal lengths. The small dial at the back of the finder has markings which indicate distances corresponding to subject distance. To use the finder, set the dial to the figure most closely corresponding to the distance from the subject. If the subject is then centered in the finder, it should also be centered on the ground glass of the camera. It is recommended that the camera be mounted on a tripod and the ground glass image be compared with the finder image to see how closely the margins of each coincide. (See fig. 49.)
6 -
8- (J
10 - -	6
-8
-	.»
15 - - 15
-	30
-50
30 — _ ioo
50°°
'00
Figure 49.—View finder and Vernier focusing scale.
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\
.XT\ Peep ' c \ sight
frame yr
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184.	Vernier focusing scale.—The graphic type of camera is fitted with a special Vernier focusing scale (fig. 49) consisting of two parts, one on the camera bed and one on the movable track. To focus, pull the camera front outward until it rests against the infinity stops. Adjust both scales until the distances coincide with the camera-to-object distance at one of the scale markings. Intermediate distances can be proportionately estimated. This scale must be used only with the regular camera lens to which it has been adjusted. It is advisable that the lens aperture be reduced as much as prevailing light conditions will permit if depth of field becomes a factor, which must be considered.
185.	Built-in shutter lock.—The purpose of this lock is to keep the focal plane shutter open and prevent its accidental release when the between-the-lens shutter is in use, such as for making synchro flash photographs. This lock is located directly below the shutter release lever and is released by winding the focal plane curtain or manually by pushing it forward.
186.	Reflex type.—Another type of hand camera is known as the “reflex” wherein a mirror is placed at a 45° angle between the lens and the focusing screen. The purpose of this device is to show the image right side up on the ground glass and so be able to focus right up to the moment of exposure. The upper end of the mirror, being pivoted, is immediately released on pressing the shutter release lever to close the top of the camera thereby preventing light from fogging the film.
187.	Range finders.—A valuable accessory to any camera is a range finder by which the operator is able to measure accurately the distance from the lens to the object. The lens-to-film distance may then be set by means of the focusing scale. If the range finder is lens-coupled, the act of measuring the distance automatically sets the lens film distance. In some range finders, the field of view is divided, one-half being displaced when the field is not in focus. In others, two complete images are visible until the correct adjustment is obtained. Like all mechanical instruments, range finders, especially when lens-coupled, sometimes get out of order and become inaccurate. Periodically, the accuracy of the range finder should be visually checked on the ground glass of the camera. If the camera is not fitted with a ground glass focusing screen, a sheet of ground glass may be placed in the back of the camera so that its surface is in exact register with the focal plane.
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Section IV
COMPOSITION
Paragraph
Purpose of composition________________________________________188
Fundamentals____________________________—_____________________189
Factors of good composition___________________________________190
188.	Purpose of composition.—a. Definition.—Composition is the arranging and spacing of objects in a photograph according to the laws of harmony and proportion, or proper arrangement of material to be photographed.
b. Method.—The proper arrangement of the image on the focusing screen is one of the most important operations in taking a photograph. In composing the photograph, the cameraman’s task is essentially one of selection and arrangement of parts through the choice of such a viewpoint and such conditions of lighting as will produce the effect desired. He begins with an empty space, the boundaries of which represent the margins of the photograph he is about to take. His problem is to arrange the image of the subject on the ground glass so that the thought he wishes to convey is clearly and unmistakably portrayed. Every photograph should have a readily recognizable subject and it should be possible for anyone seeing the photograph to understand why it was made and exactly what it illustrates.
189.	Fundamentals.—There are three generally accepted fundamentals of composition; simplicity, point of interest, and balance.
a.	Simplicity.—Simplicity means that the purpose or interest of the picture is readily recognizable and that it is not confused with a mass of surrounding objects and lines that would compete with or detract from the point of interest. For example, a person is being photographed in a garden. There are trees, flowers, shrubs, a pond, and a garden seat. If the person appeared small in the picture and no more prominent than the mass of surroundings, the composition would result in a confusion of purpose as to whether the picture represented the garden scene or the person being photographed. If the person is looking into the pond or resting on the seat, only enough of the garden should be included to support the composition. A less pictorial example of simplicity would be an object such as an automobile in front of a building. Simplicity of composition would result if there were no other objects on the ground surrounding the automobile. It would also contribute to an understanding of the picture and its purpose in showing that the automobile is the subject of the picture, if the building in the background is slightly out of focus. This will avoid lines in the background conflicting with the lines of the automo
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bile and thereby emphasize the fact that the automobile is the purpose of the picture.
b.	Point of interest.—Every picture should have a definite point of interest which should be outstanding in the composition and show clearly why the picture was made. The point of interest, also described as the subject, is best located when it occupies a position other than the center of the composition, preferably slightly below and to the right of the center. In addition to the location of the point of interest, its importance should be emphasized or supported by the lines of the picture. A line that emphasizes leads the eye to the point of interest and consequently is known as a “leading line.” It is best located when entering the picture a little above either of the lower corners. It is unnecessary that a leading or supporting line be a definite demarcation. It can be a part of the picture that suggests direction toward the point of interest.
c.	Balance.—A balanced composition is one in which the disposition of various features in a photograph gives harmony to the whole setting. Balance of composition is not accomplished by equality of mass or bulk on each side of the picture, as might be supposed. A composition is in balance when a large object on one side of the picture, preferably the right side, is opposed by a smaller object of similar nature on the opposite side. For example, a view of a building including trees will be in balance if a tree occupying much of the right-hand side of the picture is balanced by a tree or group of small trees occupying about one-third of the left-hand side of the picture. When the smaller balancing object is on the left, it is less likely to block or interfere with the leading line or entrance into the picture. Balance can also be suggestive, such as areas of sunlight or shadow, but in general solid objects are preferable. Whatever method is used to balance a composition, the balancing objects should not be too prominent or in competition with the main object or purpose of the photograph.
190.	Factors of good composition.—The following basic factors of composition apply to most types of photographs:
a.	The size of the image must conform to the picture space.
b.	The point of interest should be slightly below and to the right of center.
c.	The subject should appear as if entering the photograph.
d.	Lines of the photograph should support the main point of interest.
e.	Lines of the background should not be in confusion with lines of the subject.
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f.	Light or dark areas, especially when near the margin of the picture, will attract the eye and should not be in conflict with the point of interest.
g.	The background should not be prominent.
Section V
EXTERIOR SUBJECTS
Paragraph
Composition__________________________________________________________191
Groups_______________________________________________________________192
191.	Composition.—While the general rules of composition given in paragraph 190 can be applied to all types of subjects, there are certain rules that are applicable when photographing specific subjects.
a.	Building.—In photographing a building, a viewpoint should be selected that will show one side as well as the front. This will indicate solidity and will show both the depth and the 'width of the building. In this respect, a direct view of the corner should be avoided. A high viewpoint, or one from the full extension of the tripod, is preferable and should be such that the entrance will not be obstructed. The foreground should be in good focus and of sufficient depth to furnish ample support for the building. A foreground that is too deep will tend to give the building an elevated appearance and conversely, if the foreground is too narrow, the building will lack support. The background should be unobtrusive and usually out of focus to prevent confusion of lines of objects with the lines of the building.
(1)	Vertical lines of the building should appear vertical in the photograph.
(2)	The lens should be of as long focal length as the available distance of the camera from the building will permit to avoid abnormal perspective.
(3)	Cross lighting will show the architecture of the building to the best advantage.
(4)	A tall building should be composed vertically in the photograph. The converse is true if the building is wider than it is tall.
b.	Mechanized equipment.—Mechanized equipment includes tanks, combat cars, automobiles, and trucks. A subject of this type should be photographed from an angle which will give more prominence to the side than to the front, the viewpoint selected being sufficiently toward the front to indicate its width and show important features.
(1)	A low viewpoint will give the best perspective, show the machine to best advantage, and minimize background lines.
298620°—41---9
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(2)	The lighting should be from behind the camera and toward the subject.
(3)	When possible, the front wheels should be turned at an angle about 10° toward the camera. If this can be done, the front wheels will appear straight in the photograph.
(4)	Doors and windows should be closed.
(5)	A background that is plain or not too prominent is desirable.
(6)	The foreground should be sharp, preferably of good density, and of sufficient width to appear capable of supporting the machine.
(7)	A long focal length lens should be used. A single element of a convertible lens is preferred.
(8)	In addition to the use of a long focal length lens, distortion should be corrected by the use of the horizontal swing or vertical tilt.
(9)	The subject should appear as entering the photograph. For this purpose, the rear of the machine will be nearer to the margin of the picture than to the front.
c.	Airplanes.—The background should be plain or out of focus to avoid confusion of lines with those of the subject. The darkened interior of a hangar will usually make a good background if the airplane is placed in the opened doorway. More often the sky will form part of the background. In such case, the light from the sky should be regulated by the use of a filter. Cloud effects will thus be preserved and enhance the appearance of the photograph.
(1)	A front viewpoint should be selected and should be at such angle that the tail assembly and identification can be plainly seen.
(2)	All propellers and at least part of each motor should be shown.
(3)	The camera should be at a height that will permit the wings to cover as much of the horizon as possible.
(4)	The horizon should be level even at the expense of having the airplane tilted in the photograph.
(5)	The ends of the wings should be very close to the limits of the picture space.
(6)	Propellers having two blades should be in horizontal position. Propellers having three blades should have one blade pointing directly toward the ground.
(7)	Ordinarily the undersurface of the wings and fuselage are weakly illuminated. Exposure must be sufficient to give detail in these parts of the airplane. It is advisable to supplement illumination in these areas by the use of reflectors.
d.	Machine parts.—Parts of machines are often photographed both in their assembled position and apart from the machine. These pho
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tographs are made for the purpose of showing installation, defect, breakage or wear of a particular part, or to assist in description, identification, and replacement of the part. The details of the part should be sharp and well defined, and if a moving part, its mechanical operation in relation to adjacent parts should be evident.
(1)	Identification of the part such as by number, letter, or word, if any, should be clearly shown.
(2)	All detail necessary to the photograph must be sharp, clear, and well-defined.
(3)	When the particular part is difficult to discern because of surrounding objects it may be isolated by placing a cardboard, cloth or blotter to serve as background. This effect may sometimes be achieved by using a depth of field that includes only the particular part.
(4)	When a photograph is required that will show only a broken or damaged section of the object, the defect itself is the subject and should be so considered in the composition, focusing, lighting, and exposure.
(5)	In bright light, the natural contrast of the subject may be so great that proper exposure of the shadows is impossible without overexposure of the highlights. In such instances, a screening of the light to reduce the natural contrast is advisable. It may also be necessary to reflect light into the darker areas to secure shadow detail.
(6)	The use of a reflector may give too broad a light which will also cover the highlight area too much. This necessitates the use of a small focusing spotlight or a pocket flashlight to illuminate the shadows alone.
e.	Crash photographs.—Photographs are always made of airplane crashes to assist in determining the cause of the accident, any structural weakness, or for preservation of evidence. To cover such an assignment properly, the following photographs should be made:
(1	) A general view of the crashed airplane showing its identification number and insignia if possible.
(2	) Several photographs of damaged sections, particularly those parts which might show the probable cause of the accident.
(3	) Any landing marks which might assist in analyzing the accident.
(4	) Any damage to surrounding property which might result in a claim for damages.
(5	) All negatives made should be on as large a scale as possible.
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192.	Groups.—Military personnel may be photographed in either formal or informal groups.
a.	Formal.—The senior officer or distinguished person will be placed in the center and other officers or personnel will be placed to right and left in order of rank. However, whenever a group of the same rank or grade is being photographed, the persons may be arranged according to height, with the taller in the center. When the group is large, it should be divided into rows and placed at different levels. The space in individual rows will be such that the faces of those in the rear will not be shaded or obscured. It is essential that uniformity of position of headdress, legs, feet, and hands be preserved.
b.	Informal.— (1) An informal group is not arranged or posed in any particular order; the persons may be occupied in some general manner and not looking at the camera. For this type of photograph, a hand-held camera producing a 4- by 5-inch negative is commonly used, the negative subsequently being printed wholly or in part by enlargement.
(2) Large groups of 100 or more persons are best photographed from an elevation of about 8 to 10 feet from an extension tripod, the roof of a truck, or other suitable height.
c.	Lens focal length.—In photographing a group, the lens should be of sufficient focal length to insure that the persons in the rear of the group will not appear in perspective appreciably smaller than those in the front and will be within the vision of ordinary perspective. For example, a 12-inch lens is ordinarily used for a group up to three or four rows. With six rows, a 15-inch lens is necessary for uniform scale.
d.	Location.—Any group should, if possible, be located in shade. If shade is not available, the group should be located in such position that the members will not be facing direct sunlight. If the camera must face the sunlight or be at an angle to it which will allow direct rays of the sun to enter the lens, the lens must be shaded.
e.	Camera viewpoint.—The camera should face the center of the group with the lens at or a little above eye level with persons in the front row. The attention of all persons should be directed to some point indicated by the photographer at the moment of exposure.
f.	Exposure.—As brevity of exposure is an important factor, everything must be done to secure such desirable result. For example, select a high speed film of long scale of gradation; supplement daylight with flash if necessary; focus accurately on a point approximately two-
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fifths of the distance into the depth of the group itself with the lens at full aperture; and stop down the lens diaphragm only enough to secure sharpness of focus throughout the depth of the group.
Section VI
INTERIOR SUBJECTS
Paragraph
General_____________________________________________________________193
Buildings, halls, rooms_____________________________________________194
Personnel___________________________________________________________195
Airplanes and airplane parts________________________________________196
Installed machinery and equipment-----------------------------------197
Engineering or small object photographs_____________________________198
Groups--------------------------------------------------------------199
193.	General.—While the general rules of composition (par. 190) apply to a considerable extent in the photography of interior subjects, there are certain directions that should be followed when photographing such subjects because of the inherent characteristics. Interior photography usually requires the use of artificial light as either the principal or auxiliary source of illumination.
194.	Buildings, halls, rooms.—Photographs of interiors of buildings are required for the purposes of showing construction, repair, or alteration, and for historical record.
a.	Selection of lens.—For this type of interior photography, the selection of a lens having the correct focal length that will properly portray the subject is very important. For instance, if the subject is a hallway that is much longer than it is wide, a lens of at least 12 inches focal length should be used for a negative 8 by 10 inches. If the subject is a room or an interior of average proportions, that is, a little longer than it is wide, a much shorter focal length lens should be used. In this case, a wide angle lens of about 6% inches focus for an 8- by 10-inch negative will be satisfactory.
b.	Composition of the photograph.— (1) Vertical lines must appear as vertical in the photograph.
(2)	Avoid horizontal lines that extend across the picture.
(3)	Other lines should support the point or object of interest.
(4)	Show three walls, ceiling and floor, the upper part to be about two-thirds and the lower part about one-third of the picture area.
(5)	The viewpoint should not be directly toward a comer except for some special purpose; even then the corner vertical line should not center the composition.
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(6)	There must be an entrance into the picture. If possible, show an exit also. An entrance is any unobstructed pathway leading into the picture, not necessarily a door or arch.
(7)	Avoid large objects in the foreground that may be out of focus or detract from the main object or point of interest.
(8)	The main object or point of interest should seldom occupy the center of the composition.
195.	Personnel.—a. General.—The photography of interior subjects is often required to include persons who are occupied in some manner. For such pictures, large floodlights of sufficient power to allow instantaneous exposures are sometimes used. The method that will require the least operating equipment is the use of a hand camera fitted with synchronized photoflash.
b. Composition of the photograph.—Select a viewpoint that will show to the best advantage how the personnel is occupied. All persons should be giving their attention to the work they are performing and not be looking at the camera at the moment of making the exposure.
(1)	The point of interest should be clear and well-defined.
(2)	Sufficient surrounding area should be included to support the main feature or point of interest.
(3)	If the distance from camera to subject will not permit the composition that is desired in the final print, the negative may be masked to obtain the desired composition in printing.
196.	Airplanes and airplane parts.—a. Airplanes.—While it is unlikely that a photograph of an entire airplane will be made inside a hangar, the same rules of composition would apply as for exterior airplanes. The general illumination within the hangar may be aided by the use of one or more portable lights to assist in the illumination of the darker areas.
b.	Airplane parts.—The photographing of parts of airplanes while in a hangar is of considerable importance. Such photographs are made chiefly for the purpose of illustrating technical reports. This type of photograph must show the following features:
(1)	The part itself in sharp, well-defined detail.
(2)	Its operation and relation to surrounding parts.
(3)	Surrounding parts (especially the background) that are not essential to the purpose of the photograph should be out of focus, if possible, or eliminated entirely.
(4)	Any letters or numbers, and like features that will identify the part.
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c.	Equipment.— (1) Lens focal length.—When it is desired that an 8- by 10-inch negative be made, the camera should be equipped with a lens of 12 inches focal length. For a 4- by 5-inch negative, a lens of about 6 inches focal length will be suitable.
(2)	Illumination.—It generally will be found that the existing light of the interior of a building results in a deficiency in illumination of the darker parts of the object. This in turn will mean a considerably prolonged exposure for shadow detail. If the subject is one in which the highlights are prominent, it may not be possible to prolong the exposure for the dark parts without overexposing the highlights. A reflector may be some help in such cases. However, the best controlled system of lighting, and the one easiest to calculate the correct exposure, is by the use of a small portable floodlight in a reflector that can be moved to different positions in relation to the object.
d.	Operating directions.—(1) Depth of field.—When the part to be photographed has a greater depth of field than 5 inches, it is not advisable to attempt a 1 to 1 scale when making the negative. The distance from the lens to the object should be increased so that a slightly reduced scale will result. This reduction can be projected to a larger scale, if necessary, when making the print.
(2)	Focusing.—In focusing the image on the ground glass, it is important that a point two-fifths of the distance into the depth of the object be focused sharply at the full lens aperture. Unless this point is carefully selected, the front or rear of the object may still be out of focus when the lens is stopped to its smallest aperture. After the determined image scale has been focused on the ground glass and the lens aperture reduced to give the necessary depth of field, the extremities of the object are carefully examined on the ground glass by strong lighting for critical sharpness.
(3)	Position of floodlight in relation to the object.—Light is reflected from any bright surface at the same angle as the incident light to that surface, and consideration must be given to the angle of lighting in order to avoid “flare” which will result on a negative whenever strong light strikes a lens.
(4)	Concentration on the object.—It is always necessary that the photograph of the object itself be free from confusion of lines in the background or other parts not directly related to the main objects. This result can sometimes be achieved by using a lens aperture that will give the necessary depth of field in the object and still not place the background in sharp focus. This is not always possible if the background is close to the object. In such instances, a sheet
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of cardboard, a focusing cloth, or similar article may be used as a background. Should these practices fail to accomplish the result desired, the only remaining recourse is to block out the undesired portions of the negative which in itself is a difficult operation requiring much time and skill.
197.	Installed machinery and equipment.—a. Photographs are required of machinery, especially newly installed machines, for historical records, reports, and similar purposes. The following features should be shown:
(1)	The viewpoint should be such as to show the front of the machine and some of the side.
(2)	Show as clearly as possible the working parts and power source. If the machine is powered by a belt from line shafting, it is not necessary to show the line shafting.
(3)	If it is required that operation be shown, one or more mechanics should assume a natural pose of attention to the machine and not look toward the camera.
(4)	The photograph should be free of interferences from surrounding objects and background as much as possible.
b. General operating considerations.—Photographs of this nature usually require that the machine be isolated or free of interferences. If the installation is at a sufficient distance from the background, confusion of lines from that source will be avoided if the background is out of focus. When this is not possible, a white background should be placed behind the object and illuminated by two floodlights that are completely independent of the illumination used to photograph the machine itself. If such background is not perfectly plain or shows creases or other marks, such can be eliminated if the background is kept in motion during the exposure. A plain white floor ground should be used if the machine is not mounted as a fixture. Otherwise the floor area must be blocked out in the negative. Windows or any kind of illumination in the rear of the object should be blocked out entirely or the photograph made at night.
198.	Engineering1 or small object photographs.—a. General.—Military photographs occasionally are required of small metal objects, such as component parts of a pistol or machine gun, or aircraft parts to accompany a technical report or requisition. Such photographs must show the object as fully as possible, particularly working parts, and should indicate a number, letter, or other mark that will assist in identifying the object or part.
b.	White background.—(1) Purpose.—The objects required to be photographed will range in size from small springs, bolts, etc., to
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objects 8 inches long and 5 inches deep. Some form of isolation should be used so that very small parts will appear clearly in the photograph regardless of the fact that some of these parts may be dark or black, and some bright or white. For this purpose, a white background is used to isolate the part from what would otherwise be background interference, whether the part itself be white or black. The white background is photographed at the time the negative is made. This eliminates the necessity of attempting to block out the negative and isolate the part by hand work.
(2)	Photographing the object.—For all objects other than those requiring special treatment, such as indirect lighting or the use of one or more pola-screens, the method of operation is the same in all respects as for indoor photographs of machine and airplane parts, with the exception that the object is supported at a distance from the background.
(3)	Photographing the background.—At the conclusion of exposure for the object, it is an entirely distinct operation to photograph the background. The object is elevated or placed on a support at a distance of 6' to 8 inches from the background. If it is practicable to increase the distance between the object and background, it will be easier to obtain sufficient density in the negative to have it appear white in finished print without getting halation or impairment of the outline of the object. The method of photographing the background is very simple in itself but requires extreme care in its operation. The procedure is as follows: Bring the floodlight to a position about 8 inches above the background, at the same time tilting the reflector at such an angle that the light illuminates the background but does not strike the object (fig. 50). While maintaining this position, keep the light moving around the object so that the whole ground gets even illumination. Using the type film and floodlight previously indicated, the exposure for the background will vary in duration from 1 to 2 minutes according to the operating distance of the floodlight when making the exposure for the object. When the object is such that it can be supported at a distance from the background, the above procedure will give a perfect light-resistant negative background, saving all the time and effort necessary to block out the ground by hand work.
(4)	'White backgrounds for very small objects.—In many instances, it is required that a photograph be made of an object and the parts composing its interior. The interior parts may be so small and numerous that it is impossible to support them all at a distance from the background. In such cases, placing the objects on an elevated sheet of glass is not practicable. The best method of obtaining the desired photograph is to place the objects on a white ground in their proper
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order. A single floodlight is used at a distance of about 5 feet and is kept moving around the objects during the exposure to prevent the shadows registering too strongly. In this case a perfectly white background cannot be obtained. The light gray effect should not be objectionable.
Figure 50.—-Illumination for engineering photographs.
c.	Using two floodlights.—When a large number of small object photographs are required, a single floodlight used as the illuminant will make the operations too slow. Good negatives may be obtained by placing two 2,500-watt photo floodlights in reflectors, one on each side of the objects, at distances of about 6 feet. These lights should be mounted on adjustable stands and elevated to a height so that the light will be directed toward the objects at an angle of approximately 45°. Exposures in this case will average between 20 and 30 seconds at //45.
d.	Use of indirect and diffuse lighting.—Certain objects having bright surfaces that reflect light from many different angles cannot be photographed by any direct lighting without one or more such surfaces producing “flare.” The use of such things as putty or condensation of atmospheric moisture to dull such surfaces is inadvisable. The method of using indirect lighting from a reflector is satisfactory
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in the case of a flat surface, but this type of lighting is not suitable for uneven surfaces that reflect light at different angles in widely varying intensities. Such conditions are best met by using diffused light. To accomplish this, the bright object is enclosed in a transparent paper compartment called a “tent.” This will prevent the object from showing any reflections of surrounding objects and permit easy control of highlight reflection. The object is placed in the tent which is completely closed except for a small aperture through which the camera lens projects. The lighting system which may consist of one or more floodlights is manipulated from outside the tent to produce the desired effect.
e.	Photographing glass objects.—Glass objects may be photographed by either diffused lighting or by direct lighting, depending on the nature of the object. In either case, the appearance of the glass will be best preserved if the light source is directly above or at a slight angle to the object depending upon whether the object is flat or curved.
/. Use of light box.—A light box is an apparatus with an interior that can be illuminated. A diffused glass lid or top serves the purpose of a platform on which small objects may be placed. The objects are photographed without the interior of the box being illuminated. On completion of this exposure, the interior of the box is illuminated to give the exposure for the white background. The advantages of this method are its simplicity of operation and convenience. The main disadvantage is that for objects having convex sides or surfaces, the outline of such objects will be weakened or lost completely due to the fact that they are in contact with the illuminated surface.
g.	Photographs to show texture.—(1) It is sometimes required that the texture of objects such as fractured metal, fabrics, tile, brick, etc., be clearly shown. The success of the photograph depends upon correctly judging the angle of light to the object so as to get the proper cross lighting. The best method of illumination is to use a single floodlight, raising and lowering the light until a position is determined that will show the full form of the texture. In the required position, it will be observed that the cross lighting produces strong contrast between high lights and shadows with practically no halftones. This will result in shadows appearing with insufficient detail. To overcome this defect, a second floodlight of the same type is used on the shadow of the object at double the distance of the opposite light. The exposure for this secondary light at the stipulated distance will be approximately an additional one-sixth of the exposure. For example, if the exposure is found to be 5 minutes, the exposure
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for the secondary light will be 48 seconds, or a total exposure of 5 minutes, 48 seconds, to give necessary shadow detail and full texture rendering. (See fig. 51.) By a study of figure 51 it will be noted that a flat lighting fails to register the general contour of the subject; that a distinct cross lighting results in blocked shadows, but that a texture lighting (a cross lighting aided by a secondary light used so as to increase shadow exposure) will permit the registration of both texture and contour.
© Flat lighting—no
texture.
® Cross lighting—shadows blocked.
@ Texture lighting—detail in shadow.
Figure 51.—Cross lighting to show texture.
(2) If the object to be photographed is a piece of broken metal that has a sparkling or bright crystalline texture, it is important to use a nonhalation emulsion and also to increase the distance between the floodlight and the object.
199.	Groups.—While groups of people are usually photographed outdoors, circumstances sometimes make it necessary that this work be done inside a building.
a.	C omposition.—Composition and arrangement of the subjects follow the same rules as for outdoor groups, whether formal or informal.
b.	Lighting and camera equipment.— (1) Exposure time should be as brief as possible. For formal groups, floodlighting is best and should be of sufficient volume to permit an exposure not exceeding i/5 second. Another advantage is that the group can be observed under the light condition by which the negative will be made and checked for balance or evenness of illumination.
(2	) If a synchronized flash is used, two or more photoflash lamps should be so placed as to evenly distribute the light over the area to be photographed. Avoid the use of a single flash at the camera position as it will result in a greater exposure at the center of the group. A lighting of this sort will be flat at the center with a
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gradual verge toward cross lighting as the extremities of the coverage of the flash are approached.
(3	) If the subject is to be photographed with an unsynchronized flash mechanism, place the flash equipment in position as in the above described case. Focusing may be necessary with the aid of a light or bright object placed at a suitable position within the area to be photographed. Prior to exposure the shutter should be set for “time,” and the room darkened as much as practical. To make the exposure the lens should next be opened and the flash made, followed by an immediate closing of the lens. If the lens is opened for a prolonged period either prior to or following the flash, a troublesome exposure may be had by the general illumination within the room, which will result in movement in the photograph.
Section VII
IDENTIFICATION PHOTOGRAPHS
Paragraph
Definition and use_______________________________________________200
Placing the subject______________________________________________201
Camera __________________________________________________________202
Illumination_____________________________________________________203
Exposure_________________________________________________________204
Official portraiture_____________________________________________205
200.	Definition and use.—An identification photograph is one made for the purpose of establishing the identity of a person. Photographs of this type are used on identification cards, file cards, official records, or passports.
201.	Placing the subject.—The subject may be either standing or sitting and must face the camera in such a way that a full front view photograph is obtainable. He should be 5 feet from a white or light gray background. The subject should be relaxed and not possess a fixed expression either in the form of a grin or a too stern countenance. The hands should be at the sides and the uniform correctly worn, minus headgear. When several persons are being photographed, positive identification is obtained by photographing an identification card which is held in a suitable manner by each individual photographed.
202.	Camera.—The camera should be adjusted to a horizontal position and at such a height that the lens and the eyes of the subject are on a common level. The focal length of the lens should be approximately six times the measurement of the image of the head to avoid abnormal perspective, and should be of sufficient speed to
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allow instantaneous exposure; a speed of //3.5 or //4.5 generally being quite satisfactory. The operator should use the eyes of the subject as a point of focus. They serve as the best example of the contrast necessary to focusing and are so situated as to afford sufficient depth of field. Identification photographs are 1)4 by 1)4 inches in size, with the image of the head measuring approximately 1 inch. In the trimmed photograph, the image of the head should be approximately y16 inch from the top and midway between the sides of the picture space.
203.	Illumination.—Flat lighting is used in identification photography, consisting of two lamps in efficient reflectors. A lamp is placed on each side and to the front of the subject so that the light is directed toward the sides of the face and evenly distributed. The lamps should be close enough to the subject to afford the use of a fast shutter speed and yet not so close as to be unbearable by the1 subject. They should be 4 feet apart and 6 inches higher than the camera lens. The placement above the lens is to avoid harsh reflections if the subject is wearing glasses, and to remove the light from his direct line of vision, thus reducing the possibility of a fixed stare. The illustration specifies lamp distances and positions relative to the subject and camera (fig. 52®).
204.	Exposure.—The exposure time should be of short duration to reduce the effect of possible movement of the subject. A shutter speed of less than %5 second is not recommended. With a fixed light intensity the exposure time necessary for correct exposure is governed by the speed of the film used and the nature of the subject. Either a panchromatic or orthochromatic color sensitivity is satisfactory but for the purpose of photographing a man’s face an orthochromatic emulsion is especially recommended. Using two No. 1 photoflood lamps (as indicated in fig. 52®) with an equivalent wattage of 500 watts each, an exposure time of y25 second at //5.6 is satisfactory when using an emulsion of a Weston rating of 16 in artificial light. The subject should rest his eyes by closing them for a short period prior to exposure, to avoid blinking while the photograph is being made. The photographer should be prepared to “snap” the shutter when the eyes of the subject are open.
205.	Official portraiture.—a. General.—Pictures of officers and personnel for special purposes are oftentimes required. They differ from identification pictures in that the subject is photographed to appear to advantage. The accompanying figure (fig. 52(2)) illustrating lighting technique will be helpful to the camera operator.
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It is essential that a sufficient volume of light is available to permit instantaneous exposures of not more than %5 second at a suitable aperture. The general rules of placing the subject as outlined for
BAC KGROUND
X----
5'
4-CAMERA
LENS AND SUBJECT'S EYES ON COMMON LEVEL
SUBJECT
EXPOSURE TABLE
TYPE OF LAMPS	DISTANCE LAMPS TO SUBJECT	DISTANCE BETWEEN LAMPS	HEIGHT OF LAMPS	EXPOSURE FILM SPEED WESTON 16	EXPOSURE FILM SPEED WESTON 32	EXPOSURE FILM SPEED WESTON 64
2 *1 PHOTOFLOOO -OR 2 LAMPS OF 500 WATTS EA.	4 FT.	4 FT.	6 INCHES ABOVE EYE AND LENS LEVEL	75sec	as SEC FA	sTsec-
© Lighting for identification photographs.
Figure 52.
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,/ \
LAMP AND ____________4*_________/LAMP AND
REFLECTOR \p\	/X)/ REFLECTOR
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<'\|3ACKGR0UND \
SUBJECT |	|
BACKGROUND
ILLUMINANT y/^OOSENECK SCREEN
DIFFUSER	^J/mODELING LIGHT
MAIN LIGHT \\ f-------------
CAMERA
® Lighting for official portraits.
Figure 52—Continued.
identification photographs may be applied here with the exception of the subject’s headgear which may or may not be worn, depending upon the orders as received by the photographer.
b. Illumination.—The modeling light is placed to the side of the subject and at a height sufficient to permit a 45° tilt of the lamp when directed toward the subject. The effectiveness of this light is augmented by the use of a head screen so adjusted as to reduce the light intensity as desired on different portions of the subject’s face. The usual procedure is to reduce the light intensity between the temple and the ear and to equalize the illumination on both ears. The main light source is placed on the opposite side of the subject. Its main purpose is to soften any dark shadows and thus reduce harsh contrast. The illumination may be either diffuse or direct depending upon effects required by the particular subject. The distances at which these lights are placed from the subject are dependent upon the intensity of the illuminant and the particular portrayal of the subject as desired. The closer the modeling light is to the subject the greater its effect if properly governed by use of the screen as indicated in figure 52®. The background should be light if the subject is dark or medium, and light gray if the subject is fair. If a light or gray background is not available, the background may be illuminated with a bright spotlight. This will cause it to record light in the photograph. Rugged features, such as generally found among men and elderly people, require more modeling than will the features of a youthful and smooth countenance.
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Section VIII
PHOTOGRAPHY OF MOVING OBJECTS
Paragraph
General__________________________________________________________________206
Factors to be considered_________________________________________________207
Calculating the shutter speed____________________________________________208
Focusing the image-------------------------------------------------------209
Sensitized material____________________________________________________  210
High-speed photography for	technical studies_____________________________211
206.	General.—Objects that must be photographed while in motion include soldiers on the march, combat vehicles, motorized equipment, airplanes, troops in action, sporting events, etc. (See fig. 53.)
a.	In the photography of moving objects it is frequently desired to give the impression of motion and yet render the object with sufficient clarity as to be readily recognizable in nature and type. For example, in the case of an airplane in flight, it is desirable to use a shutter speed suffic iently short to stop the motion of the airplane but allow the blur of 1 he propeller to give a sense of movement. Similarly, it is frequently desirable to let wheels of moving vehicles be slightly blurred to indicate that they were in motion at the moment of exposure.
b.	In other cases it is necessary to show details of objects in motion, such as caterpillar treads, recoil mechanisms, truck springs, landing gear action, etc. This type of photography should render the object as sharp as possible. Certain types of subjects have moments of reduced movement as the moving part approaches center and the cameraman must be on the alert to make the exposure at the time when the probability of securing sharp detail is increased. It is sometimes helpful to swing the camera and follow a moving object in order to obtain sharp detail, even though blurring the background. Here again the impression of motion is given without sacrifice of detail. If, however, the action or motion of the vehicle is not essential to the photograph, then it can be secured better while the subject is motionless.
207.	Factors to be considered.—a. Speed.—When the moving object is such that it is necessary to prevent blur or lack of definition in the image, the exposure must be sufficiently brief so that the effective movement of the object during exposure will not be apparent The speed at which the object is moving, insofar as it affects the taking of the picture, is in reality the speed at which the image of the object travels across the film. In considering the speed of the object, both the ground distance traveled and any movement within
298620°—41----10
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the object itself should be included. For example, in the case of a horse running, the movement of the horse’s feet will be proportionately greater than the speed of the horse’s body. It is generally advisable to calculate the exposure for the most rapidly moving part which often means shortening the exposure by about one-half that required for the whole object. This in turn must not be calculated to such an extreme that all sense of motion of the object will be lost as previously explained.
b.	Angle of movement.—The image speed and therefore the permissible exposure time depends upon the speed of the subject and also the direction of its motion relative to the axis of the camera. A subject moving at a given speed directly across the field of view will require a shorter exposure than when at any other angle. When the direction of motion is at an angle of 45° to that of the camera, relative motion will be stopped by twice as long an exposure as that used for the same object traveling at 90°. Moreover, from a pictorial or compositional standpoint the 45° viewpoint is greatly preferred.
c.	Distance of object from lens.—The distance of the subject from the camera is of importance principally as it affects the depth of field. Thus, in order to secure sufficient exposure, it is desirable to photograph from a greater distance if the diaphragm must be used at its maximum opening.
d.	Focal length of lens.—The depth of field is governed by the focal length of the lens used from a given viewpoint or distance. In many instances enlargement in printing will be necessary to produce an image of the desired scale.
208.	Calculating the shutter speed.—a. Table of speeds.—A table of approximate shutter speeds adaptable to various types of subjects is shown in figure 53 for use as a guide to exposure.
b. C amerama/nl s technique.—Success in the photography of moving objects depends upon skill in handling the camera. Unless the cameraman is thoroughly familiar with his instrument and can instantly set, reset, or adjust it in the brief time allowed while a moving object is rapidly approaching, it will be found that the object will have passed out of view before the exposure can be made. In the photography of moving objects the mind of the operator is usually occupied with making rapid decisions as to exposure and position. In fact, the operator usually will be constantly shifting his position in order to secure the most favorable one and at the same time adjusting the shutter and perhaps also the lens diaphragm to give the required exposure at the new position. It is good practice to select a point in the path of the approaching object and take
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sufficient time to focus very carefully on this point. If the point selected is near and the focus is desired for as large an area as possible around the point, the lens should be stopped down to the smallest diaphragm opening at which the exposure required can be made.
TABLE OF SHUTTER SPEEDS TO RECORD SUBJECTS IN MOTION			PROPER SHUTTER SPEEDS		
			MOTION TOWARD OR AWAY FROM CAMERA	MOTION AT 'ABOUT 45° ANGLE TO CAMERA	MOTION AT RIGHT ANGLES TO CAMERA
SUBJECTS IN MOTION	APPROXIMATE SPEED OF SUBJECT IN MILES PER HOUR	DISTANCE OF SUBJECT FROM CAMERA			
LANDSCAPES INCLUDING SLOWLY MOVING WATER		BEYOND 25 FEET	l/50 TO l/lOO		
PEDESTRIANS. SLOW-MOVING ANIMALS CONSTRUCTION WORK, STREET TRAFFIC BOATING. TROOP MOVEMENTS	5-10	25 ft. 50 FT 100 FT.	1/13 5 l/65 l/35	l/265 / 135 l/65	1/400 1/200 1/100
ATHLETICS, BASEBALL, YACHT RACES HORSE RACING, MOTOR BOATS SURF, DIVING, VIEWS FROM TRAINS	20 —SO	25 FT. 50 FT 100 FT	l/335 l/l35 l/05	l/665 1 / 265 1 /l35	1/1000 1/400 1/200
AUTO RACES, MOTORCYCLES, AIRPLANES LANDING AIRPLANES. FAST TRAINS	60 AND OVER	25 ft 50 FT. IOOFT	l/500 l/335 l/l35	1 / 1000 1 / 665 1 / 265	1 /1000 1 /400
Figure 53.—Table of shutter speeds for moving objects.
(1)	The shutter speed to be used to confine the movement of the image on the plate to the desired amount can be computed mathematically. Ordinarily an image which does not have a movement greater than %0() inch is considered to be sufficiently sharp. However, when it is known that the negative is to be enlarged many diameters it is necessary that the movement of the image be restricted to a smaller distance.
(2)	The movement on the plate is greatest when the object being photographed is traveling at right angles to the lens axis. When the angle is 45° to the lens axis the movement is about two-thirds as great. Therefore, the exposure time can be increased 50 percent and the same amount of movement will result as when made at the
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faster shutter speed with the object traveling at right angles to the lens axis.
When the object is moving directly toward or away from the lens there is respectively a slight increase or decrease in the size of the image. An exposure time three times as long as that which would be necessary when the object is traveling at right angles to the lens axis will restrict this change in size so that the movement (or displacement) will ordinarily not be greater than the specified allowable movement. To compute the shutter speed to be used in photographing moving objects it is customary to compute that which would be proper when the object is traveling at right angles to the lens axis. If the movement is 45° to the axis this exposure time is increased 50 percent. If the movement is parallel with the lens axis the first computed exposure can be increased three times.
(3)	The following will illustrate how the exposure time is computed. It is desired to photograph a motorized vehicle in such a manner that the image will be 8 inches long and the movement of the image confined to y100 inch. An object 30 feet long is traveling 60 miles per hour at an angle of 45° to the lens axis. To compute the exposure time, the distance from the lens to the object must first be determined. The proportion to use is d : D :: F : A.
d—length of image D=length of object F= focal length A = distance from lens to object
Substituting known values:
8 : 360 :: 12 : A or A = 540 inches or 45 feet
Then:
Distance in inches X allowable movement Focal length X speed in inches per second
=shutter speed
Or substituting known values:
45X12X%oo	1	■ + i i/
—12 X1056 = 2346 °r aPProximately /2400 second
which would be the correct exposure time when object was traveling at a 90° angle to lens axis. Traveling at 45° to the lens axis an exposure time 50 percent greater or %6Oo second would be correct.
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(4)	It is often realized that after the exposure time for making a photograph of a moving object has been calculated, it is impossible to use it. This may be because the calculated exposure is insufficient, or because the shutter is incapable of the calculated speed. To establish a practical exposure time, it is necessary to calculate an exposure time within the range of available shutter speeds. If a decrease of shutter speed is necessary to correct exposure, the camera must be moved to a greater distance from the object in order to keep the movement of the image on the plate within the desired limit. The increase in distance is directly proportional to the increase in exposure time. For instance, in the above example, at a distance of 45 feet an exposure of %6oo second was correct. Consider that it was desired to make the exposure at %Ooo second, the distance from camera to subject would then be:
1 •
1000 ’ 1000
45: X or X=72 feet
The scale of the image decreases in direct proportion to the distance of the camera from the object. Consequently the image would be too small in the case just cited. The image may be enlarged by projection but consideration must be given to the fact that for each diameter of enlargement the effective movement on the plate is multiplied by two. In order to maintain a movement on the finished print of not more than %00 of an inch, the cameraman must reduce the actual movement of the image on the focal plane. The movement allowable is determined by the times enlargement necessary in printing.
209.	Focusing the image.—In the photography of moving subjects, it is practically impossible to keep the subject in focus, watch its approach, and trip the shutter at the critical moment. The faster the movement, the more difficult this becomes. To circumvent this difficulty, the usual practice is to prefocus an area on the ground that will be sufficient to include the required area of the subject. Allowance must also be made for the reaction time of the cameraman. Therefore the shutter control is operated at such a time that the subject will be in the area on which focused at the time the shutter opens and closes.
210.	Sensitized material.—Ultra speed films having Weston ratings of 100 or more have greatly simplified the problem of the photographer in making fast action photographs. This type of film can well be used with all conditions of daylight and up to 1/200 of a second when using photoflash bulb illumination.
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211.	High-speed photography for technical studies.—Fordetailed study of rapidly moving pieces of equipment it is necessary to have completely sharp photographs. For this reason exposures of less than ^oooo °f a second are sometimes used. Inasmuch as camera shutters are incapable of these speeds the light source itself is made intermittent creating an instantaneous flash. With such short exposures the light intensity must be extremely high in order to secure negatives of sufficient density. Gaseous discharge lamps and high voltage sparks are used to furnish light of extremely short duration. This type of photography is used in studying the stresses placed on aircraft structures, propeller torque, vibrations, landinggear recoil, gun movements, and other engineering uses.
Section IX
FLASHLIGHT PHOTOGRAPHY
Paragraph
General__________________________________________________________________212
Flashlight materials and equipment_______________________________________213
Synchro flash____________________________________________________________214
Uses of synchro flash____________________________________________________215
Reflectors---------------------------------------------------------------216
Photoflash bulbs_________________________________________________________217
Exposure---------------------------------------------------------------- 218
212.	General.—Flashlight is a form of artificial light of a highly concentrated nature. It is used generally to obtain instantaneous exposures of objects with which other types of lighting would be impractical. Flashlight can be used as a unit of illumination or as an auxiliary to either artificial light or daylight. It is especially useful for making indoor pictures as it is easily controlled and is readily adaptable to produce any degree of contrast or softness.
213.	Flashlight materials and equipment.—Flashlight can be produced by igniting a highly combustible powder in an open flash pan or by use of the photoflash lamp. Flash powder is used principally for night aerial photography and for large outdoor ground gatherings. Flash powder is seldom used for interiors because of the fire hazard, smoke, and dust. Inside the bulb of the photoflash lamp is a quantity of magnesium alloy which is explosive under certain conditions and capable of producing light. The explosive element is usually in the form of a fine wire or crumpled foil and may be ignited by electricity. Bulbs containing foil can be fired by contact with each other, one central bulb being fired electrically. Wire-filled bulbs cannot be fired by this method of contact. Photoflash
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bulbs are usually provided with some protection against bursting when fired, such as a coating of transparent medium both inside and out. Some bulbs have a safety color spot which changes color if there has been a leakage of air into the bulb. This change of color indicates that the bulb is not safe to use.
214.	Synchro flash.—Synchronized flash guns are shutter opening devices that are either electrically or mechanically (spring) operated. In principle these guns are alike although the practical application of the several types may differ. When the switch is closed, contact is made which fires the bulb and operates the shutteropening mechanism. Synchro flash may be used with between-the-lens or focal plane shutters. When using a flash with a focal plane shutter difficulty may be encountered in producing an even exposure over the entire plate. This is because the “peak” of the flash is of less duration than the time required for the shutter to act. It is necessary to use a bulb of an illuminating peak long enough to accommodate the shutter action.
215.	Uses of synchro flash.—Synchronized flash equipment is desirable for most interiors and for exteriors under poor lighting conditions. Synchronized flash may be used to great advantage in filling in the shadows present under harsh exterior lighting and is frequency used for personnel photographs made under brilliant sunlight. Its application to equipment photography under like conditions is obvious.
216.	Reflectors.—a. Some reflectors are designed to concentrate more light in the middle portion of the covering area. Such reflectors should never be used when flood light illumination is necessary. The efficiency'of any parabolic or spherical reflector depends upon five very important factors: Position of the bulb, distance of bulb from center of reflector, size of bulb in relation to reflector, the curve of the reflector, and polish of the reflector.
b.	The position of the bulb in the reflector determines the direction of the projected rays. The light-producing area of the bulb should be centered with the parabolic curve so that the light rays will be projected straight ahead. Some reflectors have an adjustable device to assist in accomplishing this purpose which, however, is only partly effective, being also dependent on the size of the bulb.
c.	The distance of the bulb from the center of the reflector has a direct bearing on the evenness of the illumination. For example, if it is too far forward, the light rays will cross giving uneven illumination and a “hot spot” at the point of crossing.
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d. The size of the bulb or light source in relation to the reflective area is also important. A reflector should be designed to accommodate a light bulb of certain dimensions. If a different size bulb is used than that for which the reflector is made, there will be a proportional loss of efficiency.
Figure 54.—Reflector efficiency.
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e. The shape of the spherical or parabolic curve governs the “spread” of the light rays projected. For example, a reflector that is shaped more like a cone than a dish will project a narrow and more concentrated beam. A dish-shaped reflector will spread the light more in the nature of floodlighting or broad illumination. Some reflectors are provided with an auxiliary ring of metal with a diffusing surface. This ring covers approximately half the bright or polished surface and serves to diffuse the outer ring of light and increase the angle of spread. The various features of the action of light in relation to reflectors are illustrated in figure 54.
217. Photoflash, bulbs.—Photoflash bulbs, or lamps, may be procured in many different sizes from the golf-ball size to the large high intensity lamps for photographing large groups and areas. A blue-coated lamp is also available for use in color photography.
218. Exposure.—a. Flash exposures, whether lamp or powTder, are not calculated in the same way as other exposures. It is obviously impossible to use a light meter. Other than the usual exposure factors, exposure is dependent upon the size of the flash used, the photographic characteristics of the flash, and the operating distance from the subject. To ascertain the correct exposure the amount of light emitted by the flash and its actinic or photographic qualities must be known. This established, the exposure is computed by consideration of the operating distance and the exposure requirements of the subject itself. Exposure tables furnished by the manufacturer of flash bulbs are of great value to the cameraman and should be used whenever bulbs of unknown intensity and spectral analysis are used.
b. As an emergency test of synchronization of flash and shutter the cameraman may fire a lamp and by looking through the lens as the shutter opens, ascertain if the flash is evident. If the flash is plainly in evidence at the highest shutter speed available the synchronization is in proper sequence.
Section X
EXPOSURE
Paragraph
Definition-------_----------------------------------------------------------219
Factors of exposure---------------------------------------------------------220
Calculating the exposure----------------------------------------------------221
Photo-electric exposure meter------------.----------------------------------222
Visual extinction meter_____________________________________________________223
Key stop system_____________________________________________________________224
Tables and guides___________________________________________________________225
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219. Definition.—A photographic exposure is the subjection of a sensitized emulsion to light. The amount of exposure a sensitized material can receive is dependent upon the actinic intensity of the light and the duration of time the light is allowed to act. Intensity times the time, therefore, equals the exposure ( 8xT=E).
220. Factors of exposure.—a. In calculating exposure the following factors should be considered:
(1)	Shutter speed and lens aperature.
(2)	Intensity of light source.
(3)	Speed of the emulsion.
(4)	Brightness range of the subject.
(5)	Color of illumination.
(6)	Development.
b.	Shutter speed.— (1) The shutter speed is the duration of time that light is allowed to pass through the lens and is dependent upon the intensity of the light source and the size of the lens aperture. For any given set of illumination conditions and film speed, the shutter speed varies with the lens aperture. The larger the aperture the faster the shutter speed.
(2)	The lens aperature is the effective area of the lens through which light is allowed to pass during the time the shutter is open. The faster the shutter speed, the larger the effective aperature for a given exposure.
c.	Intensity of the light source.—The intensity of light varies inversely with the square of the distance from its source. Light reflected from an object varies in this same ratio. The cameraman is concerned with the light which actually reaches the focal plane when he is determining the exposure necessary.
d.	Emulsion speed.—The faster the film in use, the shorter will be the exposure necessary to record the desired image. The exposure, then varies inversely as the speed of the emulsion.
e.	Brightness range of the subject.—The range of brightness in the subject to be photographed is a direct factor in determining exposure. A subject of short brightness range will require less exposure then varies inversely as the speed of the emulsion.
/. Color of illumination.—The exposure is directly dependent upon the color of light in the illumination and the color sensitivity of the film being used. For artificial light exposures, a film which has a high sensitivity to red should be used because the illumination predominates in the longer wavelength region of visible light. Artificial light exposures are longer than average daylight exposures due to deficiency of highly actinic blue light. Exposures in late afternoon
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would also be longer than in early morning and midday because the light from the sun would predominate in red.
g. Development.—The extent to which a developer will develop the shadow detail of a negative varies with different developers. This variation is so great that manufacturers of sensitized emulsions state a speed rating for an emulsion based on a definite degree of development in a specified developer. This speed rating is used in determining correct exposure and will vary if other than the recommended developer is used.
221.	Calculating the exposure.—There are three methods in general use for computing exposure; the use of exposure meters, the key stop system, and the application of exposure tables. The computing of exposures by the use of a photo-electric meter is generally conceded to be the most accurate method as the element of human error is more likely to occur when using other systems.
222.	Photo-electric exposure meter.—A photo-electric exposure meter is an instrument by which the intensity of the light may be measured and the correct exposure computed. The meter consists of three main parts as follows:
a.	A light-sensitive cell which, when energized by light, forms an electric current. The amount of this current is proportional to the intensity of the light received by the cell.
b.	A device which measures the electrical current formed and has a numerically graduated scale to indicate the amount of light incident on the cell.
c.	A movable scale for computing the exposure. The meter should never be subjected to heat greater than 140° F. in order to avoid deterioration of the sensitive coating on the cell which would change the calibration.
223.	Visual extinction meter.—The visual extinction meter operates on the principle of light transmission through a numbered or lettered disk enclosed in the body of the meter. The clarity of the characters on the disk appearing in the graduated illumination indicates the light value. After the light value has been determined, the exposure time is computed by means of a mechanical scale in which the speed of the film and the lens aperture is taken into consideration.
224.	Key stop system.—a. General.—When an exposure meter is not available, the exposure may be calculated by a system known as the kep stop which is, in effect, a means of employing the camera as a visual extinction meter.
b. Method.—To determine the exposure by this system, a camera with a focusing screen is necessary. The camera is set up and prop
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erly adjusted, with the lens set at its greatest aperature. The photographer next views the subject directly to obtain a mental impression of the illumination. When this is accomplished, the image on the focusing screen is viewed, with all extraneous light excluded. The lens is then stopped down until the intensity of the illumination in the image is equivalent to the mental impression of the subject. The aperture reached is called the kep stop. The exposure time at this aperture will vary with the film speed and is approximately equal to the reciprocal of the Weston speed rating. For example, a film with a Weston speed of 24 would have a key stop exposure time of 1/25 of a second, Weston speed 50 would give )40 °f a second, etc. If the lens must be stopped down farther than the key stop to obtain more depth of field, or opened up to obtain faster shutter speed, the exposure must be computed accordingly.
225.	Tables and guides.—a. The purpose of the exposure table is to facilitate the finding of the correct exposure in terms of shutter speed and lens aperture for different types of subjects according to the speed rating of the film used and the prevailing light condition, either daylight or artificial. The table shows how to determine exposures that are correct within the latitude of the film used, for different types of subjects, when the exposed film is processed in the manner recommended. An exposure table is shown in figure 55. While exposure tables and guides do not measure actual light values, it will be found that by exercising ordinary care and judgment in their use, exposures of sufficient accuracy may be readily determined.
Lens apertures at 1/25 second
	Brilliant subjects	Bright subjects	Average subjects	Shaded subjects
Bright sun	F/22	F/16	F/ll	F/8
Hazy sun	F/16	F/ll	F/8	F/5. 6
Cloudy-bright		F/ll	F/8	F/5. 6	F/4
Dull		F/8	F/5. 6	F/4	F/2. 8
Figure 55.—Daylight exposure table.
b. An exposure table that is provided with a movable part which is adjustable for different types of subjects under varying light conditions is referred to as an exposure guide. The speed of the film being used is considered in the calibration of the guide. Usually the part of
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the outdoor guide referring to the light condition is divided into four sections: bright sun, hazy sun, cloudy-bright, and dull. The part of the guide referring to the subject is divided into four classifications: brilliant, bright, average, and shaded. By connecting the movable part of the guide indicating the light condition with the type of subject to be photographed, the shutter speeds and corresponding / number lens openings to give the correct exposure for a particular film are automatically shown. (See fig. 56.)
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Figure 56.—Daylight exposure guide.
c. An exposure guide for artificial light exposures usually has definite light conditions and shutter speeds on a fixed scale. On a movable scale, an arrow is marked. This arrow points to the light condition. On the lower part of the scale the lens aperture is indicated for definite films depending upon the emulsion speed. Light conditions are given
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for definite types and numbers of lamps at various distances. (See fig. 57.) It is advisable for the cameraman to maintain a record of
Figure 57.—Artificial light exposure guide.
exposures. This will serve as a guide for future use of the data set forth by the exposure guide or table and will develop a sense of exposure judgment.
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Chapter 9
NEGATIVE MAKING
Paragraphs
Section I. General_______________________________________226
II.	Exposure_____________________________________ 227-234
III.	Development__________________________________ 235-242
IV.	Mechanics of development_____________________ 243-247
V.	Fine-grain development_______________________ 248-252
VI.	Negative making in tropical climates_________ 253-254
VII.	Speed processing_____________________________ 255-264
VIII.	Duplication of negatives_____________________ 265-267
IX.	Defects in negatives_________________________ 268-269
X.	Hand work on negatives_______________________ 270-272
XI.	Lettering or titling_________________________ 273-274
Section I
GENERAL
Paragraph
Importance-----------------------------------------------------------226
226.	Importance.—Negative making is the most important step in the production of a photograph. The first requirement is that the sensitized material be correctly exposed and afterward that it be developed properly. The negative, therefore, is the foundation of the photograph and when a good negative has been produced, the successful completion of the photograph is more than half accomplished. From a negative which has been thus produced, it is possible to' make any desired number of prints with comparatively little difficulty.
Section II
EXPOSURE
Paragraph
General-------------------------------------------------------------------227
Light intensities---------------------------------------------------------228
Tones_____________________________________________________________________229
Reproduction of tones_____________________________________________________230
Effect of exposure on tone________________________________________________231
The perfect negative______________________________________________________232
Effect of exposure on density_____________________________________________233
Densities with increased exposure__________________—----------------------234
227.	General.—The first step in the production of a negative is the exposure. In any photograph, there is a representation of the form of an object and of the effect of the light falling upon it. This effect
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is called “light and shade.” Correct reproduction of the outlines of the photographic image depends upon the quality of the lens. In this section, consideration will be given to the proper representation of the effect of the light falling upon the subject, which is the basic problem involved in negative making.
228.	Light intensities.—Any subject that might be photographed is composed of areas which reflect different intensities of light. The areas which reflect much light are called “highlights” while those which reflect little light are called “shadows.” Other areas which reflect more light than the shadows but less than the highlights are called “halftones.” A photograph, to represent a subject properly, must be composed of areas which will reflect amounts of light proportionate to the corresponding areas of the original subject. In the photograph of a house (fig. 58) the pipes at the top of the chimney and the white stucco between the paneling of the gables are the lightest portions of the photograph and are, therefore, the most prominent highlights. The projecting wing of the house, by cutting off the direct rays of the sun, forms a heavy shadow on part of the roof and part of the garage. This is one of the darkest shadows of the photograph. The lighter areas of the lawn are neither dark nor light but are halftones. There are many shadows, highlights, and halftones in the photograph other than those pointed out. A study of the photograph will also disclose that there are a large number of variations between the highlights and the halftones and between the halftones and the shadows. The range of shades from white to black is long. The intermediate tones between the highlights, halftones, and shadows are called gradations. Many subjects contain an innumerable number of gradations of light intensities. These fine gradations must be recorded in the negative in such manner that they will be reproduced in a print made from the negative. Such a negative is said to have good gradation. When a negative of an average subject has a good gradation, it is proof that the negative was properly made, as good gradation can be obtained only when the exposure and development have been correct.
229.	Tones.—Perhaps a clearer idea of what is meant by a “tone” can be obtained from the study of a simple subject. In the photograph of a house (fig. 58) there are many tones. However, in the picture of an eight-sided block (not considering the top of the block) (fig. 59) there are only four tones in the range from lightness to darkness. They are:
a. The side of the block directly facing the light, which is the brightest side.
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Figure 58.—Light intensities in a normal subject.
ft- The side next to the brightest which is turned slightly away from the light and is, therefore, not so bright as the first side.
c. The side opposite the direction of the light, which is, therefore, the darkest side.
d. The black background.
230. Reproduction of tones.—In order to show how the tones of the subject are reproduced, there has been included in figure 60 a cross-section view of the negative reproduced above it. From a study of this negative of the block, it will be observed that during the exposure the light reflected from the brightest side of the block was so strong that the silver halide grains were exposed through the entire depth of the emulsion. However, the light reflected from the other sides of the block was weaker and its effect on the emulsion not so great, that is, light reflected from the front of the block affected only the grains lying in the upper half of the emulsion; light from the shadow side affected those grains lying near the surface; while that from the background was insufficient to affect any of the silver halide grains. The effect of the light on the emulsion was in direct proportion to its strength, and when the negative was developed,
298620°—41----11
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only the exposed or affected grains were changed into grains of metallic silver as the figure shows. The formation of a usable image requires that a certain number of silver halide grains be acted upon by the light, not too many and not too few, but just the proper number. The length of time that the image is allowed to be projected by the lens on the film while it is in position in the camera (the exposure) controls the number of silver grains which must be affected by the light to produce the required negative image. The exposure must be just long enough to affect the proper number of silver halide grains.
Figure 59.—Highlight, halftone, and shadow.
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These light-affected grains are reduced during development to fine particles of black metallic silver which, when viewed through a high-powered microscope, resemble infinitesimal lumps of coke as shown in the photomicrographs (fig. 62).
Figure 60.—Underexposure, overexposure, and normal exposure.
231. Effect of exposure on tone.—The image in the negative consists of deposits of minute black silver grains scattered throughout the emulsion. There are deposits of these grains of various depths or densities corresponding to the intensities of the light as reflected by the different parts of the subject photographed. If the amount of the exposure has been insufficient, these deposits will not be dense enough; if the exposure has been too great, the deposits will be too thick and opaque and the tones in the subject will not be correctly reproduced. In this respect photographing an object differs greatly from viewing an object. When looking at the actual block with the light falling upon it in the same way as shown in
163
NEGATIVES
PRINTS
VNC’LR E'XPOSt'O	UW*1.	fcA»0Stl
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Figure 61.—An ideal negative and print.
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figure 60, the four tones or shades are easily seen, and just as long as the block is gazed upon, it will appear exactly as it is in the picture. The camera would see the block in this manner after a time, but then only for a little while, at the expiration of which it would rapidly begin to see it quite differently. The amount of time therefore, that the camera is allowed to see the subject during the length of the exposure is vital to the correct reproduction of the tones of the subject. This will be apparent from a study of figure 60 in which are shown a series of negatives which are respectively underexposed, normally exposed, and overexposed. In the lower half of the illustration is shown a print made from each negative. It will be noted that the highlight in the photograph made from the underexposed negative is not clear and bright as it should be, that the halftone is too dark, and that the shadow is dense and shows no detail. In the photograph made from the correctly exposed negative, the tones are such that a true representation of the block is secured. In the photographs made from the overexposed negative, it is evident that the highlight is much brighter than it should be, that the halftone is really a highlight, and that the shadow is almost a halftone; also, there is more detail in the shadow than is necessary to the true reproduction.
232.	The perfect negative.—a. A perfect negative is one from which, with a minimum effort, a print which portrays the subject in the desired manner can be secured. To produce such a print the densities of the negative must correspond to the different brightnesses of the subject.
b.	Figure 61 shows what is considered a perfect negative and a print made from the negative. Comparison of the negative and print will show how the tones are reversed and how each gradation of tone in the negative is reproduced as equal gradations in the print.
c.	In figure 62, the three small circles on the negative inclose minute sections of the emulsion which are respectively a highlight, a halftone, and a shadow. The photomicrographs show the relative number of silver grains in these different densities of the negatives.
d.	If it were possible to view a complete cross section of a negative under a microscope, the deposits of silver grains would appear not unlike a range of mountains, the highlights appearing as peaks, the shadow portions forming valleys, an,d the intermediate tones forming intermediate heights. Figure 62 shows how the grains of silver lie in the emulsion of a negative.
233.	Effect of exposure on density.—a. General.—By the density of a negative is meant the extent of the silver deposits in it which constitute the image. Density controls opaqueness or blackness and
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Figure 62.—Silver grains in various densities.
capacity for stopping or regulating the light in printing. The extent to which the quantity of silver deposited in a negative determines the amount of light which passes through the negative can be explained as follows: The deposit of silver in a certain area of a negative is such that 30 percent of the light is transmitted. In the corresponding area of another negative which had more exposure, the amount of silver deposited is twice as much. Imagine that this second deposit lies in two layers, each equal to the layer in the first negative. The first of these two layers will pass 30 percent of the light. The second layer will pass 30 percent of the 30 percent transmitted by the first layer. This will be 9 percent and not 15 percent, which amount might seem logical at first consideration. It is most important in
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HALF TONE HIGH LIGHT	SHADOW
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making negatives to realize that a slight difference in the density of any portion of a negative makes a decided difference in the amount of light that will be transmitted through this portion of the negative.
b. Correct density.—The amount of silver constituting the image determines the density of a negative. When the amount is small the negative is called a thin negative, while when the amount is great, the negative is said to be dense. Either a thin or a dense negative may have any degree of contrast. However, negatives of nearly normal density are easier to judge for printing and are generally more satisfactory.
234.	Densities with increased exposure.—a. The action of the exposure on the photographic emulsion used in negative making has been scientifically studied. Under the same conditions of light and with the same kind of plate and developer, a series of photographs were made in which the exposure for each succeeding plate was double the amount given to the preceding plate. These plates were developed for the same length of time and with the same kind of developer, and the amount of the silver deposit in each was measured. The result of this work can be graphically represented by a “staircase” (fig. 63), the steps of which, although continuous, are found not to be uniform and alike, but composed of three kinds, as follows:
(1)	Those in which the rise of each step gradually increased (period of underexposure).
(2)	Those in which the rise of each step did not increase but remained equal to the tread of the step (period of correct exposure).
(3)	Those in which the rise of each step gradually decreased (period of overexposure).
b. In other words, during the period of underexposure, the density of the negative gradually increased in proportion to the increase of exposure; during the period of correct exposure, the increase in density was in exact proportion to the increase of exposure; and fluring the period of overexposure, the increase in density gradually decreased as the exposure was increased. From this it will be seen that unless sufficient exposure is given, sufficient density will not be obtained; and on the other hand if too much exposure is given, the maximum amount of density will be obtained and at the same time the proper degree of contrast will be lost. It is only by correct exposure followed by correct development that proper density and a proper degree of contrast are obtained, and the correctness of such procedure has been verified by scientific investigations.
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UNDER CORRECT	OVER
V)	f—
Z	,	__
Q	---
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i 2 4 8 is 32__________________Exposure
Figure 63.—Density exposure relation.
Section III
DEVELOPMENT
Paragraph
General____________________________________________________________________235
Degree of development------------------------------------------------------236
Temperature coefficients	of developing solutions___________________________237
Development in relation to exposure__________________________,____________238
Contrast___________________________________________________________________239
Characteristic curves_______________________________________________________20
The nine representative	negatives__________________________________241
Time and temperature development-------------------------------------------242
235.	General.—The first of the two principal factors involved in negative making is exposure and the second is development. Since the different intensities of light form the latent image in the emulsion, the purpose of development is to change the latent image into a visible and usuable image.
236.	Degree of development.—The degree of development depends upon the type of developer, its dilution and temperature, the amount of agitation given during development, and the length of time the emulsion is allowed to remain in the solution. When only one type of developer is under consideration, the first of these factors is usually constant, which makes the time of development the most important.
237.	Temperature coefficients of developing solutions.—a. An image in an emulsion will be developed in a definite time when the developing solution is used at a certain temperature. The developing time varies inversely with the temperature. A temperature coefficient is a numerical value which can be used to compute the developing time to secure equivalent results when the solution is used at different temperatures.
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BASIC PHOTOGRAPHY	237-239
b.	Temperature coefficients are based solely on the type of reducing agent used in the developing solution. The temperature coefficient for any developing agent is constant, being little affected by the other ingredients of the developing solution or by the amount the solution is diluted. However, the temperature coefficient does vary slightly with the amount of potassium bromide in the solution and it varies slightly with different emulsions.
c.	Temperature coefficients of developers can be secured from tables, direction sheets for using developers, or determined by tests. They are usually based on differences in temperatures of 10° F., but can be interpolated for temperatures between these readings. The following are the temperature coefficients for several commonly used developing agents based on 10° variations from standard
temperature.
Metol__________________________________________ 1.	3
Hydroquinone___________________________________ 2.	5
Meto]-hydroquinone----------------------------- 1.	9
Pyrogallic acid________________________________ 1.	9
d.	An example of the application of temperature coefficients is: The developing time for a developer used at a temperature of 70° F. is 1 minute. When used at 80° F., the developing time will be 60 divided by 1.9 or 32 seconds. When the solution is used at 60° F., the developing time will be 1.8 times 60 or 1 minute, 54 seconds.
238.	Development in relation to exposure.—The exposed film may be underexposed, correctly exposed, or overexposed; and development in relation to each of these three kinds of exposures may be for the proper length of time, or less than, or more than, the proper length of time. The nine different results thus obtained furnish a comprehensive study of both the factors entering into negative making, namely, exposure and development.
239.	Contrast.—When an exposed film, being developed, is examined soon after the action of the developer has become apparent, it will be found that the difference in density between the heaviest and thinnest part is not great. However, after development progresses this difference continues to grow, and as development is nearing completion, the difference between the densest portion of the negative and the less dense portion will be very much greater than it was at the beginning of development. This difference is called contrast. When it is excessive, the negative is termed “hard” or “contrasty,” and when it is insufficient, the negative is called “flat,” “soft,” or “lacking in contrast.” When development is prolonged
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beyond the point where the desired contrast is achieved, contrast will continue to build up until it becomes excessive. A print from a negative that lacks sufficient contrast resembles one from an underexposed negative in that both photographs appear dull and fail to show the natural graduation from highlights to shadows. In a print from a negative that is too contrasty, there is an equally unnatural rendering of the subject in that the highlights are too bright and strong in comparison with the halftones and shadows, and the result is a harsh representation of the subject.
To sum up the contents of the last few paragraphs, it should be remembered that the amount of detail in the shadow portions of the negative is regulated by the length of exposure; that although the degree of normal contrast in a negative is exactly fixed by the nature of the subject, the actual contrast produced in a negative thereof is regulated by the degree of development so that the actual contrast may be insufficient because of lack of development or it may be excessive because of overdevelopment. It should also be remembered that density is the result of exposure plus development. A study of the chart describing the characteristics of the nine representative negatives, paragraph 241, and figure 65 will assist in understanding the effects of exposure and development in negative making.
240.	Characteristic curves.—Figure 64 shows the characteristic curves which result when a negative is developed for 8 minutes and when developed for 12 minutes. From the curve, it is seen that the gamma of the negative developed 12 minutes will be higher than that of the one developed 8 minutes.
<>----EQUAL RISE---------•!
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55	'	'	r—JX+MIN.DEV.
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Figure 64.—Time-gamma comparison.
241. The nine representative negatives.—a. General.—The exposure of any negative may have been insufficient, correct, or too great. Similarly, the amount of development may have been
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insufficient, correct, or too much. Therefore, any developed negative can be classified as to exposure and development into one of nine types. Figure 65 shows these types of negatives. In making the illustration one set of three negatives was purposely underexposed, another was correctly exposed, and a third set was considerably overexposed. One negative from each set was developed for one-half the normal time, another negative from each set was given normal development, while the remaining three negatives were developed for double the normal developing time. Characteristics of the individual negatives are tabulated below.
	U nderdeveloped	Normally developed	Overdeveloped
Underexposed			
Detail	 Density	 Contrast		Insufficient	 Insufficient	 Insufficient		Insufficient	 Slightly lacking _ Normal		Insufficient. Slightly lacking. Too much.
Normally exposed			
Detail	 Density	 Contrast		Slightly lacking _ Slightly lacking. Insufficient		Correct	 Correct	 Correct		Correct. Too much. Too much.
Overexposed			
Detail	 Density	 Contrast		Too much	 Correct or too much. Insufficient		Too much	 Too great	 Too great		Too much in shadows and halftones. Highlights blocked. Decidedly too much. Too great.
b.	Exposure.—Upon studying figure 65, it is seen that it is impossible to secure shadow detail in an underexposed negative even when the negative is overdeveloped. Also that there is a surplus of shadow detail in an overexposed negative even when the negative is underdeveloped. From these observations, it can be correctly assumed that the exposure forms the image in the emulsion while development brings out the image.
c.	Contrast.—The degree of contrast in a negative depends upon how long the negative was developed. Figure 65 shows that the contrast of all the underdeveloped negatives is insufficient and that of all the overdeveloped negatives is too great.
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d.	Density.—The density of a negative is dependent upon both exposure and development. However, figure 65 shows that a badly underexposed negative will have insufficient density even though it
Figure 65.—Nine representative negatives.
172

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be decidedly overdeveloped. Also, that an overexposed negative will likely have sufficient or even excessive density although the development was insufficient, and that an overexposed negative which has been normally developed is quite dense, while if overdeveloped, it will be excessively dense. In fact, it is impossible to secure an exceedingly dense negative unless it has been decidedly overexposed and when the density of a negative is too great it is most often the result of overexposure and not because of overdevelopment.
e.	Importance of proper classification.—Too much emphasis cannot be placed on the importance of learning to classify negatives correctly as to exposure and development. The exposure and development of a negative are seldom exactly correct. In fact, the latitude of emulsions is such that it is of little importance if the exposure and development is not exactly correct, but it is of greatest importance that the photographer be able to recognize in a negative any variation from correct exposure and development so he can make correct changes in the ensuing negatives. If he is unable to recognize deficiencies in negatives, he will be inclined to make increasingly greater errors in exposure and development.
242. Time and temperature development.—a. The time and temperature method is based on the fact that a developing solution at a definite temperature will develop a given negative to a definite contrast (gamma) in a given time. This time will vary for different types of emulsions.
b.	The recommended temperature for most developing solutions is 65° F. Best results are obtained at this temperature, but it is sometimes necessary to use developing solutions at a lower or a higher temperature. Most developers will function satisfactorily at a temperature as low as 55° F. and as high as 80° F. A few developers, known as tropical developers, can be used at higher temperatures.
c.	The developing time to use at different temperatures in order to secure equivalent results can be computed by using the temperature coefficient of the developing solution or from time-gamma temperature charts.
d.	A time-gamma temperature chart is a chart which shows the developing time necessary to secure the desired gamma or, conversely, the gamma which will result at different developing times at different temperatures. A separate chart is generally used for each different developer and emulsion. A chart may have a curve which is characteristic of only one type film or it may contain curves for several types. Figure 66 shows a typical chart. This
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chart shows the minutes of development necessary to obtain a gamma of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 at any temperature between 55° and 90° F. This chart is for a standard fast panchromatic film when developed in a certain developing solution. The times given are for intermittent agitation of the solution. If constant agitation is used, the developing time can be reduced. Intermittent agitation is considered as agitating the emulsion at approximately equal intermissions 10 times during the time the emulsion is being developed. Constant agitation means continual agitation. This is usually secured by mechanical means when developing in tanks, or by constant rocking of the tray in tray development.
1 | VTWWIIIIIHlIHIlIIHlmF 85  ------------------------------------- 30
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2	3	4	5	6 7 8 9 10	15	20	25 30 35 40
TIME OF DEVELOPMENT
Figure 66.—Time-gamma temperature chart.
Section IV
MECHANICS OF DEVELOPMENT
Paragraph
Methods________________________________________________________243
Marking films for identification-------------------------------244
Developing in trays____________________________________________245
Developing cut films in tanks__________________________________246
Drying rooms___________________________________________________247
243.	Methods.—a. Cut film negatives are developed either in trays or in tanks. The tank system of development is the best method, especially when there are large quantities of negatives.
b. Short lengths of roll film can be developed in trays, suspended in tanks, or wound in reels having spiral grooves and developed in
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BASIC PHOTOGRAPHY
tanks. Aerial film is usually developed in a tank, being reeled from one spool to another by an electric motor during development.
244.	Marking films for identification.—It is sometimes necessary to mark exposed films before development so that the developed negative can be identified. Ordinarily, film holders are numbered and notes made of any information pertaining to specific film numbers. Some film holders have a stenciled number in the corner which is imprinted on the film during exposure. This number coincides with the number on the exterior of the holder. When the number is not placed on the film during exposure, films can be marked by the following methods:
a.	Placing identifying mark on the edge of a definite corner by placing the negative emulsion upon a rigid support and marking by means of a blunt pointed pencil having a lead of medium hardness or by means of a stylus.
b.	Using ticket punch. When a large number of films must be identified, the punch marks can be in code or several punches making different shaped holes can be used.
c.	It is somewhat difficult to use any of the above methods in absolute darkness, as it is difficult to confine the markings to the edge of the film. When large numbers of films are to be marked, it is advisable to cut a corner from a metal shield the same size as the negative. This can be used as a guard and guide. Films should be marked in the corner next to the notches. This facilitates locating the identifying marks on the negative.
245.	Developing in trays.—a. Types of trays.—Stainless steel trays are generally used for all the solutions used in tray development although enameled steel, rubber, or glass trays may be used.
(1)	The best practice is to use trays only slightly larger than the negative. This prevents the disarrangement of negatives. There is more danger of scratches when films lie in the tray in a haphazard manner.
(2)	The tray for rinsing need be only slightly larger than the negative. The tray for the fixing bath should be at least twice as large as the one used for the developer.
(3)	If a safelight is used, the tray for the developer should be placed about 30 inches from the safelight, the tray for the rinse bath to its right, and the tray for the fixing bath to the extreme right. The trays should be about 4 inches apart to prevent splashing of one solution into another.
b.	Mixing solutions.—The fixing solution should be mixed first, then the rinse bath. The developing solution should be mixed last.
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c.	Mixing the. developing solution.—The developing solution may have been mixed at using strength in which case it is only necessary to measure out and bring to the correct temperature the desired amount of solution. If the stock solution of developer must be diluted for use, the proper amount of water should be measured of the same temperature as that to be used for the developing solution. The diluted, solution should be stirred to assure uniform density and temperature after which the temperature is verified by a thermometer.
d.	Retaining temperature.—It is extremely important that the temperature of the solution remain constant while it is being used. Any change in temperature must be anticipated and necessary arrangements made to keep it uniform. Methods that can be used for this purpose are suggested in chapter 3.
e.	Handling -films in the developer.—(1) As six 8- by 10-inch films are the most that should be developed together in a tray, the method used to develop this number is as follows:
(a)	Have all solutions ready, place film holders in a systematic arrangement, set timer for proper developing time, and turn out lights.
(6)	Remove films from holders, placing them in a neat pile, emulsion down, on a clean surface. Place film, emulsion up, in left hand in a fan-like arrangement. Start timer. With right hand, slide first film, emulsion up, in the solution. Rock tray once or twice. In about 5 seconds, place the second film in the solution by pulling it, emulsion up, from left to right through the solution. Care must be exercised not to damage emulsion of film underneath. Pull the first film out of the solution, permitting the edge of the top film to squeeze lightly the solution from the emulsion of the bottom film. The first film is placed back in the solution in the same manner as the second film. The process is then repeated, which places the first film again at the bottom. This operation, while seemingly complicated, will not occupy 5 seconds time. Five seconds after the second film is placed in the solution the third film should be added in the same manner as the second. The operation is repeated, changing the positions of previously inserted films each time a new one is added, taking pains that when the sixth film is added, the position of each film (according to its number) is known.
(LTER
Figure 67.—Film drying cabinet.
negative. When a negative is set to dry at high temperature and in a very humid atmosphere with no appreciable circulation of air, it may require a number of hours for it to dry. On the other hand, extremely slow drying may cause an increase in graininess. For this reason, it is necessary to dry miniature film negatives rather rapidly, 30 minutes being sufficiently long.
Section V
FINE-GRAIN DEVELOPMENT
Paragraph
Factors affecting grain size______...____________________________________248
Type of film emulsion____________________________________________________249
Developing solutions_____________________________________________________250
Degree of development----------------------------------------------------251
Density--------------------1_____________________________________________252
248.	Factors affecting grain size.—The following factors determine the size of the silver grains in a finished negative:
a.	Type of film emulsion.
b.	Type of developing solution used.
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c.	Degree of development.
d.	Density.
249.	Type of film emulsion.—The size of the silver grains is an inherent quality of the emulsion. As a rule slow emulsions are fine grained and fast emulsions are coarse grained. However, truly fine negative can be obtained only by using a fine-grain emulsion and developing it in a fine-grain developer. Fine grain in a negative is essential when it is necessary that extremely minute detail be registered or when the negative is to be used for making prints of many diameters enlargement. Insofar as the size of grain is concerned, negatives satisfactory for most purposes can be secured by using emulsions which are not especially fine-grained and developing them in normal developers.
250.	Developing solutions.—a. With the exception of para-phenylenediamene, there is no reducing agent which will develop silver grains to a smaller size than will other agents. While this reducing agent will produce extremely fine grain, it is in disfavor because it causes skin poisoning and will not produce negatives of sufficient density and contrast.
b.	It is necessary to use more alkali with some developing agents than with others, but fine-grain developers must include a developing agent which requires little acceleration. Metol is a developing agent of this type and is often used in fine-grain developers.
c.	A fine-grain developing solution not only must have a small amount of alakali, but will give better results if a mild alkali such as borax or sodium metaborate is used. When a normal amount of alkali is used in a developing solution, the gelatin is softened to such an extent that the silver grains will shift positions and form into clumps of grains which will appear as, and in effect will be, large-size grains.
d.	Sodium sulfite has a slight solvent action on silver halides. In a developer, the sodium sulfite dissolves portions of the silver halide grains. This prevents clumping to some extent and causes the developed grains to be of smaller size. The solvent action increases with the amount of sodium sulfite so that fine-grain developers generally have large amounts of sulfite.
251.	Degree of development.—In development, grain size decreases with dilution so that a diluted developer will result in fine grain in comparison with the same developer at full strength. Contrast and speed, however, are also decreased with dilution, so it is necessary to sacrifice some characteristic to better another. As the
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time of development is prolonged and other factors are constant, grain size increases and therefore is directly proportional to gamma.
252.	Density.—The size of the grains varies in the different densities of a negative, being most apparent in large, uniform areas of halftones.
Section VI
NEGATIVE MAKING IN TROPICAL CLIMATES
Paragraph
Storage of materials_______.-------------------------------------------253
Methods________________________________________________________________254
253.	Storage of materials.—The constant high temperature accompanied usually with great humidity of the climate encountered in some localities, particularly the Tropics, requires that special precautions be taken with respect to the storage of some photographic chemicals and especially of all photographic sensitized materials. Directions concerning the storing and shipping of photographic materials and chemicals are covered in Technical Order 24-1-1.
254.	Methods.—a. Courses to follow.—Either of the two courses may be followed when developing at high temperatures: Bringing the temperature of the water and necessary solutions down to standard temperature by cooling methods; or using a special developer, hardening bath, and fixing bath at the existing temperature.
b.	Cooling water and solutions.—-When a refrigerator is available, the best method of maintaining a supply of cold water is to lead a section of the water supply pipe through a coil in a refrigerator. If this method is used, the refrigerating apparatus through which the coil is run must necessarily have a capacity commensurate with the amount of cold water required. When only small quantities of cold water are needed, ice or dry ice placed directly in the water is a satisfactory method of cooling. The developer may be mixed with this cold water or ready-mixed developer may be cooled by placing a container of it in a bath of cold water. A solution may also be cooled by placing a container of it in a bath of water and then dissolving hypo in the water. Hypo lowers the temperature of water in which it is being dissolved.
c.	Developing.—Plates and films after being exposed should be developed as soon as possible, especially in a tropical climate. Otherwise there may be a loss of density and on developing they may assume a mottled appearance. If the film is new, this is not so likely to occur, but in the case of film which is from 6 to 12 months old, it is
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not advisable to delay development for more than 1 or 2 days. Before development, all solutions should be brought as nearly as possible to the same temperature. It is most convenient generally, to bring all solutions to the temperature of the wash water. Up to a temperature of 75° F., the regular instructions for development should be followed, modifying the time of development in proportion to its temperature. If an acid fixing bath is employed containing an excessive amount of hardening agents, it is possible to exceed this temperature, although there is danger of pinholes due to the liberation of gas within the film by the action of the acid in the fixing bath on the sulfite and carbonate in the developer absorbed by the film. At temperatures up to 85° F., a strong, rapid developer should be used in conjunction with a chrome alum fixing bath, although the usual kind of acid fixing bath, containing potassium alum, often proves satisfactory. At temperatures up to 95° F., a developer of the kind described should be used in conjunction with a formalin fixing bath. At 95° F., if the negatives are lifted to and from the various solutions by means of the fingers, the emulsion is apt to become separated from the base at the edges; this is called “frilling.” When negatives are supported in film hangers during development, fixation, and washing, this trouble will not be encountered. When developing at high temperatures, negatives must be rinsed only for 2 or 3 seconds. Extreme care must be exercised in handling the negatives during the first few minutes of fixation because of the danger of damaging the extremely soft emulsion. All solutions should be at temperatures within approximately 5° F. of one another.
d.	High temperature developing solutions.—A developer used for developing negatives at high temperatures is usually concentrated so the negatives will be developed in minimum time. Sometimes it is necessary to use additional potassium bromide because some developing agents will cause chemical fog at high temperatures. Although amidol and paraminophenol hydrochloride are often used as reducing agents in tropical developers, metol and hydrochinon are also often used. Many tropical developers include sodium sulfate to repress swelling of the gelatin.
e.	Rinsing.—A negative, after being developed at a high temperature, should be rinsed for 2 or 3 seconds and then placed in a chrome alum hardening bath for a few minutes. The negative must be gently agitated when first placed in the bath. If the emulsion is extremely soft, the rinsing in water may be omitted. Formulas for tropical developers are included in appendix I.
/. Fixing.—When the temperature does not exceed 85° F., a fixing bath containing potassium alum (white) or a chrome alum fixing bath
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must be employed. At higher temperatures, a bath containing formalin must be used. This type fixing bath can be used as high as 95° F. Negatives should be fixed for 15 minutes. The formulas for these fixing baths are included in appendix I.
g.	Washing.—Negatives should be washed 10 or 15 minutes in running water or should be handled in five or six changes of water involving the same time. Radical changes in temperature between the fixing bath and the wash water should be avoided.
h.	Drying.—The negatives should be dried in a cool room. Ample circulation of air will prevent reticulation and hasten drying.
Section VII
SPEED PROCESSING
Paragraph
Purpose________________________________________________________________255
Equipment for photography----------------------------------------------256
The developer------------------------------------.---------------------257
Chrome alum hardening bath---------------------------------------------258
Fixing bath____________________________________________________________259
Preparation for quick processing_______________________________________260
Making the print_______________________________________________________261
Fixing and washing the print___________________________________________262
Drying the print-------------------------------------------------------263
Time required__________________________________________________________264
255.	Purpose.—Quick processing of both ground and aerial negatives is frequently required by the exigencies of military operations. The purpose of speed processing is to produce a usable print in the shortest possible time.
256.	Equipment for photography.—Any camera using cut film or film pack may be used. Roll film processing by this method is impractical because of the extremely short development.
257.	The developer.—a. In this type of work a highly concentrated developer, using a caustic alkali such as sodium hydroxide, is essential. For formula and mixing directions, see appendix I. This developer has good keeping qualities and should be kept in two glass bottles, one being for used solution. After use it may be returned to the container which should be filled each time from the unused solution and tightly corked.
b.	While this developer has been used successfully at 95° F., it is recommended that the working temperature be maintained at 80° F. It is not diluted, and the film should not be rinsed in water prior to development. The film is developed at 80° F. for 10 seconds and then transferred to rinse water of the same temperature for 10 seconds.
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BASIC PHOTOGRAPHY	257-260
There are two important reasons for the rinse time equaling the development time:
(1) The action of the strong alkali must be tapered off gradually.
(2) Prevention of dichroic fog which is a characteristic of caustic alkali processing unless remedial measures are taken.
258.	Chrome alum hardening bath.—-As a caustic alkali developer has an abnormal softening action on the gelatin of the film, a hardening bath should be used, especially in hot weather, after rinsing and just before the negative is placed in the fixing bath. The chrome alum hardening bath deteriorates rapidly, and should, therefore, be freshly mixed every day, or if many films are being processed, two or three times a day. The film should be agitated in this bath for 30 to 40 seconds and allowed to remain in the bath about 2^ minutes.
259.	Fixing bath.—While there are formulas for rapid fixing baths, their working life is short and the time saved by their use is so small as to be practically negligible. The regular acid fixing bath is best to use for this type of work. If the temperature of the freshly prepared fixing bath is 80° F., the film will clear in 1 minute, 50 seconds, provided it is kept in agitation during the process. The clearing of the film is all that is necessary to produce a satisfactory print. After the print is made, the negative should be returned to the fixing bath to complete fixation in the regular manner.
260.	Preparation for quick processing.—Prepare all working solutions in advance, if possible, so that delays in production of the work may be avoided. The following set-up, a diagram of which is shown in figure 68, may serve as a ready reference:
a.	Have the developer ready and checked for temperature.
b.	Place rinse bath close to developer and check temperature.
c.	Prepare fresh chrome alum hardening bath at same temperature and place it next to rinse water bath.
d.	Place freshly prepared acid fixing bath at a convenient distance from the hardening bath.
e.	Separated a short distance from the fixing bath is the print developer.
/. Next in line is the print rinse or short stop bath.
g.	The print fixing bath is placed at the end of the line. It is advisable to have a separate bath for this purpose at the correct print fixing temperature of 65° F.
h.	Lastly, a wash tray for negatives, this may be placed next to the negative fixing bath.
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261.	Making the print.—As soon as the negative has been cleared of its milky appearance, it is given a brief rinse to remove the surplus hypo. Without draining the water from the negative, place it on the printer glass and lay a sheet of very thin cellophane over it. The sheet of cellophane should be at least three times the area of the negative, free from wrinkles, and should lay flat on the negative. Air is removed by drawing a squeegee with light pressure over the cellophane surface to bring the wet negative into perfect contact with the glass. Care must be taken to see that no water remains on the cellophane to come in contact with the printing paper and cause it to stick. Errors in exposure may be minimized and time saved if three or four prints are made at different exposures. The prints are then, developed simultaneously for normal time and the best one selected.
262.	Fixing and washing the print.—The print is immersed in a fresh fixing bath at 65° F. for 1 minute. While fixation will not be complete, it will remove enough of the unexposed silver to prevent immediate fading. The print must then be washed for 1 minute in fast running water to remove sufficient hypo to prevent the print from being sticky when finished. A print which has been fixed and washed in this manner will not be permanent. If a permanent print is desired another one, fixed and washed for the correct length of time, should be made.
263.	Drying the print.—The alcohol burn-off method is best in this case. Immerse the print in alcohol for about 20 seconds, then pin it to a stick and set it afire. The print must be waved in the air while the alcohol is burning off. It will then be pliable and can be pressed flat. If the print is required to be entirely dry and not pliable, it must be left in the alcohol until the image is visible through the back of the print. Then burn off as before. This method will leave the print with a natural gloss. If a glossy ferro-typed print is required, proceed as follows: Immerse the print in alcohol until the image begins to appear through the back of the print. Then ferrotype print on clean tin in the usual manner. Place tin aside for 3 minutes for print to set. Then apply draft of air from fan. The print should fall from tin in about 2 minutes or total drying time of about 5 minutes.
264.	Time required.—A working time of about 8 minutes is required to deliver a quick work print. (See fig. 68.)
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Film
Caustic soda speed DEVELOPER TEMP 80“F DEV.TIME: 10 SECS RINSE TIME 10 SECS.
CHROM ALUM
HARDENER
ACID • HYPO
Print
PRINT
DEVELOPER
RINSE WATER
ACID HYPO
TEMP 70° F
RINSE- 5 SECS
Figure 68.—Diagram—speed processing.
Section VIII
DUPLICATION OF NEGATIVES
Paragraph
Purpose___________________________________________________265
Methods___________________________________________________266
Sensitized	material_____________________________________  267
265.	Purpose.—Negatives are duplicated for the following reasons:
a.	To have a reserve negative in case the original is lost or damaged. This is especially important when it is impossible to make a new negative by rephotographing the subject.
b.	To facilitate printing large numbers of prints. When it is necessary to make large numbers of prints from a negative, it is often advisable to make several duplicate negatives which can be printed simultaneously by several printers.
c.	To allow distribution of negatives. There are many times when it is desired to distribute negatives for printing in different locations. The desired number of duplicate negatives can be made and distributed where desired. It is often necessary in Air Corps photography to send duplicate negatives to different stations for making prints to be used for instructional or publicity purposes.
d.	To improve defective negatives. Many negatives to be duplicated are of incorrect density or contrast. Other negatives are of a type which would require much dodging when prints are made from them. All of these defects can be corrected when making a duplicate negative. Another type of negative that can be improved by duplication is one which must undergo a large amount of etching. Etching is a difficult operation for many photographic technicians. To avoid the necessity of etching, a positive can be made from the negative.
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The parts of the positive which correspond to the areas of the negative which need etching can be retouched. This will give the same effect as etching the negatives.
266.	Methods.—A positive can be made from a negative or a nega-ative from a positive by any of the following methods: Using a contact printer, projecting in a projection printer, and photographing the negative or positive while it is being illuminated by transmitted light reflected through it.
a.	Contact printing.—When the negative is of the desired size, the easiest method of duplicating is to use the contact printing method. Since film emulsions are much more sensitive than paper emulsions, the printer should be equipped with a rheostat in order that the intensity of the printing light can be reduced. If a rheostat is not available, a blotter can be placed over the ground glass of the printer. The edge of the blotter should be taped to prevent any light which does not pass through the blotter from striking the negative. When it is desired to dodge the negative, any method practiced in contact printing can be used. It is more difficult to obtain contact between a negative and a film than it is between a negative and a piece of sensitized paper. For this reason, when a contact printer is used to make positives from negatives or vice versa it is essential to observe special precautions to effect good contact.
b.	Projection printing.—When it is desired to make a duplicate negative of a size different from that of the original, the duplicate negative can be enlarged in a projection printer. Some projection printers can also be used for duplicating negatives smaller in size than the original. When the projection printer is not equipped with a rheostat for regulating light intensity, small lens apertures must be used.
c.	Photographing the negative.—This method gives superior results and has an advantage in that the size of the duplicate negative can be regulated easily. A large board with an opening of the desired size is used to support the negative. The negative is placed with the emulsion side facing the lens in this opening. It is held flat by a piece of thin clean glass on each side. Lights are placed so they illuminate a large piece of cardboard or blotter behind the negative. This will reflect an even light over the negative. The exposing of the positive is accomplished in the same manner as exposing a copy negative. A negative can be made of a positive in the same manner.
d.	Preserving details of original.—It is essential that the positive used in negative duplication contain as much detail of the original
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negative as possible. This necessitates that the positive be of low contrast. It should have no trace of chemical fog. Best results are obtained when a nonstaining developer is used.
267.	Sensitized material.—a. Although all types of emulsions can be used for duplicating negatives, one which is slow and noncolor sensitive is preferable. Using an emulsion of this type will permit longer exposures and will allow the emulsion to be developed under a safelight which will furnish sufficient illumination to develop by inspection.
b. Duplicating film.— (1) There are three distinct types of photographic films which are used for duplicating negatives. The first type is an extremely slow film which has a long scale. When this type film is used, it is necessary to make a positive and to make the duplicated negative from the positive.
(2) The second type duplicating film is used to make duplicate negatives by direct reversal. This means that the film is exposed through a negative and a duplicate negative obtained without making a positive. The process is as follows: The film is exposed through the negative. After it has been developed the metallic image is bleached out. The film is then exposed to the light. When developed the image will then be negative. Positives also can be duplicated by this process.
(3) The use of the third type of duplicating film for making duplicate negatives involves an entirely different principle of photography. This principle is that if a photographic emulsion is sufficiently exposed an image reversed in tones from one obtained by normal exposure will form when the emulsion is developed. This phenomenon is called solarization. The duplicating film is so made that a solarization occurs with comparatively short exposures. When exposed through a negative a negative image can be developed. Duplicate positives can also be made by this direct method.
Section IX
DEFECTS IN NEGATIVES
Paragraph
General-----------------------------------------------------------------268
Cause and prevention----------------------------------------------------269
268. General.—The best photographic practice is always to endeavor to conduct operations so as to avoid errors and defects. The proper selection and storage of materials, care in operation of the camera or apparatus, the correct preparation of solutions, proper condition of trays and containers, and the conscientious following
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of operation methods that are known to produce satisfactory results, will insure against error to a great extent. However, mistakes are made and if the operator can locate the causes of errors, he can avoid them in the future.
269. Cause and prevention.—The more common defects or errors in negative making are listed in alphabetical order below for easy reference as to cause and remedy or preventive. The procedure followed in finding the cause of a defect in a negative in hand should be systematically conducted. Often several descriptions will apparently fit a certain defect and the correct cause must be determined in order to learn how to correct it and prevent its recurrence. The real cause may be determined by recalling the circumstances surrounding each operation in the production of the negative and reducing by process of elimination the number of possible causes of the defect at each step in production until the true cause is revealed. In studying the defects in negatives, it will be noted that almost none of the remedies given is corrective, but are preventive only, so that the necessity of careful work in the preparation of a negative is essential.
a.	Abrasion marks or streaks.— (1) Appearance.—Fine, black lines usually resembling pencil scratches and running in the same direction.
(2)	Cause.—Friction on the emulsion of the film caused by improper handling or storage at some time between its manufacture and development. These streaks may be readily produced by laying two films emulsion to emulsion and sliding one across the other when particles of dust are present between the sensitized surfaces.
(3)	Remedy.—Great care should be taken in the storage of the film and other sensitized material. The boxes containing such supplies should be stored on end in order that no pressure is exerted on the surface of the emulsion. Care should also be taken not to rub or drag a piece of sensitized material over a rough surface, either before or during development.
b.	Air bells.— (1) Appearance.—When an air bell occurs during development, it shows as a small transparent spot. Sometimes a minute dark streak leads from the spot. When the negative is rocked in a tray the streak leads from the spot; the streak projects from each side of the transparent spot in the direction the tray is rocked. If the tray is rocked in two directions, the streak will form a cross with the transparent spot in the center. When the air bells occur in tank development, the dark streak usually forms at the lower edge of the
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transparent spot. When the air bells occur in the fixing bath, they show as small round dark areas.
(2)	Cause.—The transparent spots which occur in the developer are caused by bubbles of air on the surface of the emulsion which prevent the developer coming into contact with the emulsion. The darkened streaks are the result of the excess oxidation of the developer caused by the air in the bubble. The dark spots which occur in the fixing bath are caused by the pocket of air holding the fixing bath away from the emulsion which allows a slight continuation of development.
(3)	Remedy.—Immerse film carefully and thoroughly in the developing and fixing solutions; move film during development and fixation in order to break up and prevent air bells. Water always contains some air and when there is a rise in temperature, this air is expelled and gathers in the form of small bubbles on the inside of the tank and also adheres to the surface of the film during the preliminary stages of development. The amount of water needed for development may be allowed to stand for several hours at the temperature required for use before beginning developing operations.
c.	Black spots.—See Spots.
d.	Blisters.— (1) Appearance.—Blisters on negatives resemble the familiar ones which arise on the human skin from slight burns.
(2)	Cause.—Blisters are caused by fluid or gas formed between the emulsion and the film support when the solution has become too warm and has loosened the gelatin from its support. They are also produced by a developer and fixing bath that are both strongly concentrated so that in changing a film from one bath to the other, there is a formation of gas between the emulsion of the film and its support. Blisters are frequently caused by insufficiently rinsing the film after development and placing it directly in a fixing bath having strong acid content. Another common cause of blister is allowing water from the faucet to flow directly on the emulsion side of the negative.
(3)	Remedy.—The description of the causes of blisters indicates the manner of the avoidance of these defects.
e.	Blurred negative.— (1) Appearance.—Indistinctness or lack of definition in the negative image.
(2)	Cause.—The subject was not properly focused on the film, there was movement of the camera or of the subject or through lack of proper adjustment, a portion of the film was not flat in the focal plane of the camera when the exposure was made. A blurred effect is sometimes produced by moisture or haze on the lens or a dirty lens.
298620°—41----13
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(3)	Remedy.—Care in focusing and in holding the camera; keeping camera in proper adjustment and lens free of moisture or dirt.
/.	Brown spots.—(1) Appearance.—Brown or sepia-colored spots or small areas on the negative.
(2)	Cause.—Brown spots are produced by an oxidized developer or by fine particles of chemicals settling on the film prior to development. This defect may also occur during the washing of the negative from rust or other impurities in the wash water.
(3)	Remedy.—Avoid an exhausted or oxidized developer. Do not use the developing laboratory for the mixing of chemicals. Filter the water used for washing. (See Spots.)
g.	Crystalline surf ace.— (1) Appearamce.—The surface of the emulsion of the negative possesses a crystalline appearance suggesting frost on a window pane.
(2)	Cause.—Insufficient washing after fixing. Hypo remains in the film and crystalizes.
(3)	Remedy.—Sufficient final washing.
h.	Dark, lines.—(1) Appearance.—These lines must be divided into two distinct classes; those dark lines which run from dark areas to the more transparent areas of the negative, and those lines which run from the more transparent areas to the darker areas. In both cases the lines are wider, not as clean-cut, and not as nearly parallel as abrasion marks.
(2) Cause.—The first class is caused by insufficient agitation of negative in tank development. The cause of the second class is supposed to be of an electrolytic origin.
(3) Remedy.—For the first class, more frequent agitation of negative during development. The remedy for this class aggravates the defect in the second class. The only known remedy is to remove all the film hangers from the tank four or five times during the developing period, holding the hangers in a bunch, and allowing the corner of the bunch of hangers to rest on the edge of the developing tank for 10 or 15 seconds.
i.	Excessive contrast.— (1) Appearance.—The negative record of the high-lights and even of some of the halftones of the subject are in density greatly out of proportion to the record of the shadows, with the result that in a print made from the negative the subject has a strained, hard, and otherwise unnatural appearance.
(2)	C erase.—Overdevelopment.
(3)	Remedy.—Obvious.
j.	Fading tendency.— (1) Appearance.—Sepia or yellow-colored stains or areas in the negative.
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(2)	Cause.—Incomplete fixation, usually the result of insufficient washing. Remnants of the fixing bath left in the emulsion continue their action and in time this defect appears.
(3)	Remedy.—Always fix and wash the negatives fully and properly. Final washing is as important as any other operation in negative making.
k.	Finger marks.—(1) Appearance.—Imprint of fingers on the negative.
(2) Cause.—Impressing wet or greasy finger tips on the emulsion side of the film before or during development or fixation. If the mark is merely an outline of the finger, it was caused by water or grease on the finger; if dark, by developer; and if transparent or light, by the fixing bath.
(3) Remedy.—Keep the hands clean and dry when handling dry film. The natural oils of the body are sometimes present sufficiently on the finger tips to constitute the grease referred to above. Handle film by the edges. When the fingers have become wet with water or solution, wash and dry them before attempting to handle film. Keep the hands out of the fixing bath as much as possible, but whenever it becomes necessary to place them in the solution, always wash them thoroughly before handling the film.
I.	Flatness.—(1) Appearance.—Insufficient contrast between the highlights, halftones, and shadows in the negative reproduction of the subject.
(2)	Cause.—Flatness in the negative usually results from underdevelopment, but the subject contrast or lighting may have been flat.
(3)	Remedy.—Continue development for the proper length of time to reproduce the contrast of the subject.
m. Fog.—Fog is a deposit of silver which does not form part of the image. It may be very dense or only a slight veiling. It may occur on local parts of the negative or it may darken the entire negative. Fog increases the density and decreases the contrast of a negative. Fog may be divided into four types: Aerial, dichroic, light, and chemical.
(1) Aerial.—(a) Appearance.—Slight veiling of the negative or parts of the negative exposed to air during development.
(5) Cause.—Exposure to air during development, especially when hydrochinon is used as a reducing agent. Most frequently occurs in freshly mixed developers, especially those containing excessive amounts of hydrochinon or alkali. Developers containing formaldehyde or minute traces of copper or tin in the developing solution are also likely to cause aerial fog.
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() To reduce the prominence of defects or unretouched portrait negatives or to make rough retouching less prominent.
() Blisters and frills.
(c) Stretching of prints.
(
Figure 77.—Making lantern slides with a camera.
(3) By copying.-—When slides are made from prints, a copy negative must first be obtained. This copy may be procured in the usual manner of copying. A lantern slide plate may be used as the negative medium and, if made to the proper size, contact-printed. If a negative print is copied, the result will be a positive without the procedure of printing.
365. Processing the slide.—a. Developer.—Lantern slides are developed in developers similar to those required for bromide papers. Because of the wide range of contrast often desired, two formulas are generally recommended by the manufacturer, one producing normal contrast and warm tones and the other producing cold tones of higher contrast. (See app. I.)
ft. Development.—A lantern slide plate should be slid into the developer so it will be quickly and evenly covered by the solution. Development should usually be prolonged to the maximum or near
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maximum allotted latitude of development to insure full contrast, brilliancy of the image, and appreciable highlight density. The progress of development may be observed by examination of the image by transmitted light as apparent from the back of the plate. This examination may be accomplished either by direct light from the safe-light or by reflection from a suitable white tray.
c.	Fixing and washing the slide.—Slides should be fixed for at least twice the time required to clear and should be washed in running water for a period not less than 20 minutes. They should be carefully sponged prior to drying to prevent the formation of water spots.
366.	Finishing the slide.—a. Masking.—The usable area of a 3%- by 4-inch lantern slide plate is approximately 1 inch less than its length and % inch less than its width. In the preparation of slides for projection, at least % inch on each end and % inch on the long sides should be masked. Any extraneous matter outside the actual picture space should also be masked.
b.	Binding.—To protect the emulsion surface from damage, a cover glass is placed over the emulsion side of the plate. It also serves to strengthen the completed slide. Prior to binding, all glass surfaces must be thoroughly cleaned and both cover glass and masked slide must be completely dry. To bind a lantern slide, proceed as follows: Cut a strip of binding tape 15% inches long; lay face down and moisten the back thoroughly; when limp, turn the gummed side up and moisten this side. Now lay the strip, face up, on blotting paper; place the edge of the slide with its cover glass in position on the strip so that one end of the strip is in the center of a side of the slide and cover glass; then press them down firmly on the strip. Next, turn the slide and cover over on the strip, and over again, and at each movement press the slide and cover while held together firmly on the strip, running the finger along the edge of the binding tape so as to cause it to adhere to the slide and its cover. Next, press the sides of the strips firmly against the glass, pressing down the corner to make a neat joint. Now turn the slide over once more so as to join the ends of the binding strip and make neat joints at the corners by mitering or clipping out the corners of the binding tape, being sure to rub the edge of the binding tape down firmly before pressing the sides of the strips against the glass. A special revolving type of lantern slide vise may be used to hold the slide and cover glass in contact, thus leaving both hands free for the binding.
c.	Marking.—A mark, usually a small paper disk, is pasted in the lower left-hand corner of the emulsion side of the finished slide when the image is in an upright position. It is known as the “operator’s
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thumb spot” and is used to facilitate the insertion of the slide in the projector under operating conditions. The rule is to grasp the slide with the thumb of the right hand on the thumb spot. Insert the slide in the lantern-slide carriage from the right-hand side of the projector. The image is then inverted and the emulsion side of the slide is toward the projection lamp.
Section III
FILM SLIDES
Paragraph
Micro-copies____________________________________________________________367
Use---------------------------------------------------------------------368
Printing----------------------------------------------------------------369
Developing______________________________________________________________370
Finishing_______________________________________________________________371
Masking_________________________________________________________________372
367.	Micro-copies.—A micro-copy is a miniature-sized reproduction. Micro-copies are essentially film slides and are used to project an image in much the same manner as lantern slides. Although they may be made on any small emulsion surface, they are generally photographed on standard-size 16-mm or 35-mm motion-picture positive film. Emulsions of special color sensitivity, speed, and resolving power are manufactured for the purpose.
368.	Use.—Film slides are often used for instruction purposes and the presentation of data to audiences. They also have a wide range of uses in photographically recording various records and documents, such as identification work, the collection of important data, the dissemination of information, and the recording of laboratory and research activities. A great many micro-copies can be made on one small roll of film and filed in a small container. This method of filing has decided advantage over the filing of original data, such as newspapers, books, photographs, or lantern slides.
369.	Printing.—Micro film slides are not always printed, as the original copy is often used in projection. If they are printed, the best method is to use a motion-picture printer.
370.	Developing.—Dodging is practically impossible on such a small area and careful manipulation of exposure and development is therefore essential. Because of the extremely small-scale image, the full efficiency of the lens and emulsion used must be maintained in order to satisfactorily record the image. Therefore, some form of sensitometric control of development must be employed. (See app. I for developers.)
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371.	Finishing*.—Film slides, if projected from a roll, are so made that they are ready for projection. If bound individually, they are generally mounted on cardboard of a size and shape to suit the projector.
372.	Masking.—Prints or similar material used in film-slide making should be masked so as to exclude all extraneous material. Any further masking during the process of manufacture is therefore unnecessary. If original negatives are made directly from the subject photographed, as in the case of an outdoor scene, on material similar in size to that of the finished slide, extraneous matter should be excluded from the photograph.
Section IV
COLOR TRANSPARENCIES
Paragraph
Definition_______________________________________________________________373
Use______________________________________________________________________374
Exposure and development_________________________________________________375
373.	Definition.—A color transparency is an image made with a natural color emulsion.
374.	Use.—Color transparencies are designed to be viewed by transmitted light and are made in various sizes to suit a particular need. The larger sizes are intended for viewing by direct transmitted light and the smaller sizes are intended for projection purposes. If projected, they are mounted on cardboard or glass of a size and shape to suit the projector, but they may be in a roll and projected in a manner suited to roll projection. Color transparencies are often used in the production of separation negatives in color printing processes.
375.	Exposure and development.—The development of direct color emulsions is a reversal process which affords a very short latitude of exposure. It is therefore essential that exposures be determined with a high degree of accuracy. Processing should be accomplished with strict adherence to the manufacturer’s recommendations.
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Chapter 13
COLOR PHOTOGRAPHY
Paragraphs
Section I. General____________________________________376-377
II.	Methods of reproduction___________________ 378-379
III.	Illumination_____________________________ 380-382
IV.	Exposure and development_________________ 383-385
V.	Application------------------------------- 386-388
Section I
GENERAL
Paragraph
Definition_________________________________________________376
Types______________________________________________________377
376. Definition.—Color photography is true orthochromatic rendition; that is, the reproduction of objects in their natural colors and color brightnesses. Color is the visual interpretation of the various waves of visible light. White light is the simultaneous perception of the visible colors, red, orange, yellow, green, blue, and violet.
377. Types.—Color photographs, as in black and white photography, may be either transparencies or prints. Transparencies are positive photographs on film or glass which are viewed by light passing through the photographs toward the observer, or more suitably, by projection on an appropriate screen and consequent reflection of light in the form of the image. Prints are generally thought of as positive photographs on paper base which must be viewed by reflected light.
Section II
METHODS OF REPRODUCTION
Paragraph
Additive and subtractive processes__________________________378
Color printing______________________________________________37g
378. Additive and subtractive processes.—The two methods of producing color photographs are termed “additive and subtractive.” Additive processes are based on the principle of mixing or adding primary color, while subtractive means that certain colors are produced by absorption or subtraction of secondary colors.
a.	Additive method.—(1) This method of color synthesis is concerned with the mixing or adding of primary light colors. Any two primary colors, when mixed, form a secondary color. Blue and red in combination form magenta. Green and red form yellow, and
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green and blue form blue-green or cyan, as it is commonly called. When the three primary colors are mixed in equal proportion the combination is white. When two primary colors are coupled to form a secondary they are in equal proportion. By varying the proportion of each primary, it is possible to obtain the various shades of the secondary colors. When the additive process is used in color photography, the photograph must be viewed by transmitted light because the process is suitable only for making transparencies. All screen processes employ this principle of color synthesis.
Figure 78.—Additive process (mosaic screen).
(2) A commonly used additive method of color reproduction as a transparency is the “screen process.” There are many such processes, but the underlying principle is the same in each. A screen process is one in which a colored screen is incorporated with the film and is placed on the side of the film base opposite the emulsion. The exposure is made through the base of the film and consequently must pass through the screen in exposing the emulsion. The screen is composed of filter elements of microscopic size and in the three primary colors, red, green, and blue. These tiny filters separate the colors reflected from a photographic subject into their respective positions in the image. (See fig. 78.)
b.	Subtractive method.—(1) General.—In subtractive processes, the resultant color is the result of dyed or toned images which are superimposed. Generally, three images dyed or toned in the secondary colors, yellow, blue-green, and magenta, are used (fig. 79). These are also called complementary colors. White light on entering such a combination of images will have certain colors absorbed or subtracted in proportion to the amount of overlap of color within the layers. For instance, if only two layers contained color, such as magenta and blue-green, at a small section of the image and the
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magenta is not too dense, the green and red will be absorbed or sub-stracted and blue will be the resulting color. A magenta image will subtract green, a blue-green image will subtract red, and a yellow image will subtract blue. The amount of subtraction depends upon the intensity of the color at any one part of the image in that layer.
This principle of subtraction of color is used in all color printing and also the Kodachrome process of making transparencies.
(2) The Kodachrome process.— («) Kodachrome film is composed of three layers of light-sensitive emulsion coated on regular film base which has an antihalation backing. A cross section of Kodachrome
RAW FILM
COLOR POSITIVE
Figure 80.—Cross section of Kodachrome film.
270
|R E~D	| |G R E E~N | [y[E ~L~L~O|W
ADDITIVE COLOR	SUBTRACTIVE COLOR
ZX	• A
YELLOW	YELLOW
Figure 79.—Subtractive process.
^YELLOW IMAGE
—MAGENTA IMAGE
"■"BLUE-GREEN IMAGE
''SAFETY FILM SUPPORT
BLUE SENSITIVE EMULSION
GREEN '• RED «	"
ANTIHALATION -BACKING
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film is shown in figure 80. The surface emulsion is sensitive to blue and violet only; the second emulsion is orthochromatic, sensitive to blue, violet and green. A yellow filter dye, incorporated between the first and second emulsion layers, absorbs violet and blue so that the second emulsion responds only to green. The third emulsion is sensitive to red but not to green.
(A) This film, after exposure, is first developed as a negative. The three images thus formed are bleached out and the residual silver halide exposed and developed in “coupler” developers. The resulting images are positive and dyed with colors complementary to the colors recorded by the individual emulsion layers. The image in the top layer formed by blue light is transformed into a yellow positive; the image in the center layer formed by green light is transformed into a magenta positive; and the image in the bottom red sensitive layer is transformed to a blue-green positive. Where these dye images overlap each other, they produce, when viewed by transmitted light, different colors depending upon the proportion of color in the overlapping images. Where the images do not overlap but there is dye present in one image, the color of the dye itself is evident. At a point where none of the layers have dye, white light will result; at a point where all three layers have a full quantity of dye, no light is transmitted and black results; and when each layer contains a proportionate amount of dye not in full quantity, neutral gray is evident.
379. Color printing.—a. In color printing processes, three negatives are made, each one through a different filter. The filters used are red, green, and blue, the primary colors. These filters have sufficient overlap in transmission so that the entire visible spectrum or color range is covered. From each of these negatives, a separate positive is made. The positive image is formed by exposure through the thin portions of the negative which represent the parts of the subject which were of such a color or colors to cause little or no exposure in the negative. Since these portions of the negative cause the positive exposure, the positive image necessarily cannot be dyed with a color similar to that of the filter through which the negative was made, so they are dyed a color which absorbs the filter color. For example, a negative made through a red filter will appear thin at those parts of the image corresponding to blue and green in the subject. The positive made from this negative must then be colored blue-green which absorbs red. In like manner, the green filter negative will produce a positive which will be colored magenta; and the blue filter negative a positive which will be colored yellow. These colored images are bleached before the dyeing process and no silver remains. The images
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are on film base and must be transferred in some manner to paper to obtain a single print consisting of three superimposed images which, in conjunction, and correct color proportions, reproduce the subject in natural color. The method of transfer of images varies with the process of printing being used.
b. The three principal color printing processes in present use are the wash-off relief process, the chromatone process, and the carbro process.
(1)	Chromatone (toning).—Positives are made on special stripping paper from the tricolor negatives. These positive images are toned chemically to produce images of the required colors which are complementary to the colors of the filters through which the negatives were made. These colored positives are stripped from their bases and superimposed on gelatin-coated paper to make the final print, or may be superimposed on a clear base to produce a transparency.
(2)	Wash-off relief (imbibition).—Positives are made from the separation negatives on special film and an image of tanned or hardened gelatin produced. The exposure of the positive is made through the base of the film leaving the image next to the base. The image is developed and followed by a bleaching bath which hardens the gelatin around the image and leaves the unexposed emulsion unhardened. The silver image is also bleached completely. The unhardened emulsion is then washed off in hot water which dissolves it. The remaining gelatin, which composes a relief image on the base, is next placed in an acid hardening fixing bath. This relief image on film base is called a “matrix.” By dyeing one of the relief images with the proper color and placing it in close contact with gelatin coated paper, the dye transfers to the paper. The gelatin on the paper has been chemically treated to “imbibe” the dye, hence the term “imbibition.” (See fig. 81.) The next matrix is dyed and superimposed in register over the first transfer. The third matrix is dyed and the colored image transferred in the same manner as the second matrix. The three-colored images in superimposition on paper produce the colored print. With proper handling, the color reproduction can be made quite accurate. This process has an advantage for production work, in that a great many prints can be made from one set of matrices since the final print is a result of dye transfer. As in the chromatone process, the three dyed matrices may be superimposed without dye transfer to make a transparency.
(3)	Carbro (colored pigment).—This method involves the formation of relief images composed of colored pigment. The pigment is incorporated in gelatin in the manufacture. These pigment images
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BASIC PHOTOGRAPHY	380-381
are superimposed to form the print or transparency, and the entire process must be repeated for each print or transparency. The process is rather long and delicate but gives excellent color rendition.
! HtlH !
FILM BASE 1 ONE Of THE THREE
VFR—>--------1-------1------MM TRICOLOR SEPARATION
SILVER-1--------1----1------NEGATIVES
WASH-OFF RELIEF FILM
EXPOSED _____--------------------------- YELLOW oyeo EMULSION
SILVER GRAINS	TiiA'iuWI___________________EXPOSURE LIMITED TO
SURFACE
DEVELOPED L	_	DEVELOPED TO
SILVER	SILVER P0SITIVE
TANNED .---------------- .-------------- TANNING BLEACH
GELAWIN T -1.............1	*_______
SOFT GELATINE---J
I SOFT GELATIN
TANNED .------------------ ,------------1 WASHED OFF
GELATIN LEFT 1---------I-----1	(MATRIX)
[................... „	I DYED MATRIX
DYED GELATIN
WE Trn°xTlt|NTED ~*f~’ ■: L -z	tcph' A. / ' J GELATIN COATED
CELATIN	RAPER BASE | PAPER
| DYE ALL TRANSFERS
NO DYE	I------TO PAPER
TRANSFERRED	PAPER WITH TRANSFERRED
IMACE	DYE IMAGE
Figure 81.—Steps In wash-off relief process.
Section III
ILLUMINATION
Paragraph
General____________________________________________________________________  380
Artificial	light_____________________________________________________________381
Daylight---------------------------------------------------------------------382
380.	General.—By any process of color photography, correct color reproduction is directly dependent upon the distribution of color emitted from the source of light. Both the screen processes and the Kodachrome process have two specific emulsions, one for artificial light and one for daylight use. Daylight contains a great amount of blue light, whereas artificial light is deficient in blue in comparison.
381.	Artificial light.—Emulsions made for use with artificial light are sensitized for use with certain types of tungsten illumination and the use of other than the recommended source will result in improper color balance. The specific type of illumination to be used for a particular emulsion is generally specified. If more than one
298620°—41--18	273
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lamp is used, the others should be of the same type. For instance, Kodachrome type A is corrected for use with photoflood lamps, and any lamps of different color emission would disrupt the color balance of the finished photograph.
382.	Daylight.—Emulsions made for use with daylight should be used only with light sources having color emission equal to that of daylight. There are only certain hours of the day when daylight illumination is correct for this film. These hours on the average are from 9:30 AM to about 3:30 PM depending upon the location on the earth’s surface, weather, and season. Filters have been devised by the manufacturers whereby photography with color film may be accomplished at any time of day by application of the filter designated to change the color distribution to that recommended for the film. Other filters have been prepared for use with artificial light film in daylight, or daylight film in artificial light, or for using artificial light film with artificial light sources which differ from the recommended source.
Section IV
EXPOSURE AND DEVELOPMENT
Paragraph
Cameras__________________■________________________________________383
Exposure___________________________________________________________384
Development_______________________________________________________385
383.	Cameras.—In exposing direct color film, such as that using a screen process or Kodachrome, any camera may be used if it has a color corrected lens with normal aberrations eliminated. The lens must be so corrected that the primary colors (red, green, and blue) will be focused very close to the same plane for accurate results.
a.	When three negatives are made with the appropriate tricolor filters, one of four distinct methods may be employed:
(1)	Exposure with a one-shot camera which makes all three pictures at one time through the lens (fig. 82). The films are used in the camera in separate positions and two of the negatives may be made either by reflection of light or by application of a bipack film.
(2)	Three separate exposures with each of the tricolor filters. These exposures can be made with an ordinary cut film or plate camera by changing holders and filters for each exposure.
(3)	Three separate exposures with a camera having a “repeating back” whereby the film can be changed rapidly for each exposure.
(4)	Separation negatives made from direct color film using a contact or projection printer and appropriate tricolor filters. This
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383
Figure 82.—One-shot cplor cameras.
method is of particular use when prints are required from existing transparencies.
b.	Of these four methods of making separation negatives, the first is the most satisfactory. However, special films or plates must be used in one-shot cameras and the cameras are costly. The second method is slower and cannot be used where there is any possibility of movement of the subject during the time necessary to make the exposures. The chief advantage of this method is that it does not require a special camera or special films. The third method is better than the second in that the time necessary to make the three exposures is decreased. The fourth method usually requires the use of a good enlarger and a special set of filters but is quite satisfactory. It has an advantage in that color prints can be produced entirely in the laboratory.
275
RED FILTER
FILM__________
BLUE FILTER
I * i


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384.	Exposure.—a. Direct color film has very little exposure latitude. The maximum tolerance for superior photographs in color is one-half a normal f stop on either side of the correct exposure. This small variation in exposure latitude necessitates the use of an accurate exposure meter in determining correct exposure. Inspection of image brightness on a ground glass screen is not accurate enough for color photography. Overexposure or underexposure beyond the recommended latitude will result in incorrect color reproduction.
b. In making separation negatives, the filter factors must be taken into accurate consideration. Overexposure or underexposure in one or more of the negatives will result in unbalanced results in the positives and consequent poor color balance in the final transparency or print. For accurate results the factors of the filters to be used should be determined for the film employed in making the negatives and with the light source to be used in the photography.
385.	Development.—a. In processing photographs made by a screen process, a method called “direct reversal” is used. After exposure, the film is developed in a recommended developer, and a negative image produced. This negative is placed in a bath called a bleach which completely reduces the silver image, changing it to a transparent compound of silver which is not sensitive to light. The film is then exposed to any good light source for a sufficient length of time to obtain complete exposure in the formerly unaffected portions of the emulsion which still contain sensitive silver bromide. The next operation is to develop this exposed emulsion to obtain a positive silver image in “reverse” of the negative image.
b.	As in any reversal process, overexposure of the original is ascertained by too thin highlights, while underexposure is evidenced by darkened highlights and dense shadows. Correct exposure is essential in order to obtain the proper proportion of highlight density between positive and negative for accurate results. In competent hands, direct reversal is both simple and rapid. The time needed is somewhat longer than that required for ordinary negative processing, but the finished photograph is a positive ready for use either in projection or by direct observation.
c.	Kodachrome film is processed by the manufacturer because of the complications encountered in obtaining the dyed images in the triple layer. This entails a loss of time in obtaining color transparencies by this method.
d.	Separation negatives are developed in ordinary developers. They must, however, be developed to the same contrast in order to obtain correct color contrast in relation to the separate colors in
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BASIC PHOTOGRAPHY
volved. Too much contrast in a negative will result in an excess of a particular color in the shadows in the print because the shadows will receive too much exposure in the positive. This variation in contrast will be more apparent in the highlights due to the low highlight densities which would be present in a print.
Section V
APPLICATION
Paragraph
General______________________________________________________386
Aerial photography___________________________________________387
Ground photography_________________________________________  388
386.	General.—a. Since color photography is in a sense still in the initial stages, there are a great many obstacles to be overcome for accurate color reproduction. To produce an accurate print in color requires a great amount of knowledge and skill. The time required to produce such a print is decidedly long by any existing process. For these reasons, color photography at its best is in the production of transparencies.
b. Of the two common methods of making transparencies, the subtractive process is the most suitable. The additive process is not so satisfactory because the amount of light absorbed by the color screens renders the image dark and somewhat dull unless a powerful light source is used. In the additive process which employs screens, a granular effect or pattern is produced due to the composition of the screens. In projection, the definition or sharpness of the image is materially affected by this pattern. It is difficult to make good color prints from additive color transparencies for this same reason.
387.	Aerial photography.—Color photography is especially applicable in the interpretation of aerial photographs.
a.	The recognition of road conditions is simple in a color photograph, since the actual surface of a road would reflect its own color, thereby making identification of the material easy. Whether the surface was macadam, cement, gravel, dirt-, or any other material would be fairly obvious, whereas in black and white photography the distinction of the various shades of gray is depended upon to recognize the material.
b.	Depth is more apparent, even in a single photograph, because of the fact that actual color difference between objects is easily distinguishable. This makes the measuring of heights comparatively easy because the color of most objects differs from the shadow so that the actual length of the shadow could be more definitely determined, and
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from this length and knowledge of the time when the photograph was made plus direction of the airplane’s flight, the actual height of the object is a simple computation. In black and white photography, the shadow blends with the object making calculation less accurate.
c.	In wartime, the greatest use of color photography is the detection of camouflage as it is difficult to produce artificial color to match the colors in nature. Artificial color records differently from natural color, so that the contrast between the two is obvious. Painted shadow, artificial leaves, or any other contrivance used in producing camouflage is apparent. The depth, newness, or use of trenches are distinguishable in color photographs.
388.	Ground photography.—A photograph in color will show things as they occur naturally and not as the photographer can make them by retouching or any other similar device. It will be more pleasing to the eye and more realistic than any black and white photograph.
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BASIC PHOTOGRAPHY	389-390
Chapter 14
LABORATORY OPERATIONS
Paragraphs
Section I. Functions within	the unit___________________ 389-393
II. Materiel------------------------------------ 394-398
III. Operation___________________________________ 399-419
Section I
FUNCTIONS WITHIN THE UNIT
Paragraph
General_______________________________________________________________  389
Administrative section___________________________________________________390
Photographic files_______________________________________________________391
Supply, repair, and transport	section___________________________________392
Photographic production section_________________________________________393
389. General.—The efficient operation of a photographic laboratory unit requires a logical grouping of all the functions of the unit into subdivisions (fig. 83) which may be called sections, details, or be otherwise designated; the assignment of suitable personnel to each section; and the operation of each section in coordination with the other sections. A logical subdivision of a photographic unit would be into four sections, as follows:
a.	Administrative.
b.	Photographic files.
c.	Supply, repair, and transport.
d.	Photographic production.
I LABORATORY COMMAND
| PHOTO. FILES |--| ADMINISTRATION"]
| PROD. RECORDS [ | SUPPLY ]~| CAM. REPAIR [
-----1 PRODUCTION
COPYING |[ FILM PROCESSING]] PRINTING |
[ MOSAIC ASSEMBLY || CHEMICALS || FINISHING ]
Figure 83.—Photographic unit functional chart.
390.	Administrative section.—The administrative section is charged with the maintenance of administrative records and the rendition of administrative reports. The discharge of this function is covered in detail in Army Regulations.
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391.	Photographic files.—The maintenance of negative files, the titling and plotting of negatives, the compilation of records and index maps, and the rendition of reports related to the results of photography are the functions of photographic files.
392.	Supply, repair, and transport section.—This section is responsible for requisitioning, housing, and issuing photographic equipment and supplies; rendering reports concerning materiel; maintaining materiel records; repairing and testing cameras; and the tactical control of allotted transportation.
393.	Photographic production section.—This section is charged with negative processing, including lantern slides and films; printing, including contact, restitution, transformation, enlargement and reduction ; stereograms, reconnaissance strip and mosaic assembly; and mosaic, map, and document reproductions.
Section II
MATERIEL
Paragraph
General_________________________________________________________________394
Laboratories____________________________________________________________395
Procurement of equipment and supplies___________________________________396
Loan of equipment_______________________________________________________397
Records_________________________________________________________________398
394.	General.—The principal items of materiel issued to the photographic unit include portable or mobile photographic laboratories, supply trucks and motorcycles; developing, printing, enlarging, restituting, transforming, copying, and other laboratory apparatus; photographic film, plates, paper, chemicals, and many small items of accessory equipment.
395.	Laboratories.—a. Types.—There are three general types of housing provided for photographic laboratories: permanent laboratory buildings; portable laboratories, or temporary buildings operated with portable equipment; mobile laboratories.
(1) Permanent.—Permanent laboratories are used at permanent bases. Buildings of substantial construction are designed and provided for the housing of photographic laboratories at all peacetime air bases. However, the technical equipment for the operation of these laboratories is portable, with the exception of sinks and utilities, and so-called permanent laboratories must be prepared to evacuate and set up operating facilities in another location upon short notice.
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BASIC PHOTOGRAPHY
(2) Portable.—Portable laboratories are used in garrison or in the field. They are capable of being transported readily by normal ground or water facilities, and some types by air.
(a) By air.—These laboratories are constructed of light-weight tents with especially designed light-weight compact technical equipment. Others are small, cabinet type darkrooms capable of closing into a compact carrying case, and are complete, self-contained units which may be used in aircraft or merely transported thereby.
(&) Other than by air.—Laboratories portable by air may be moved by normal ground and water transportation facilities. However, larger tents than those designed for air transportation may be used with the standard technical equipment. The use of standard technical equipment with improvisation of local existing construction into darkrooms and workrooms is considered a very practical form of a portable laboratory.
(3) Mobile.—Mobile laboratories are used in garrison or in the field. A laboratory structure capable of mobility on land, water, or in the air, is termed a mobile laboratory. It may be capable of limited photographic production while enroute, or of full capacity operation within a short time after establishing a new base. The lack of an adequate water supply reduces the quantity of production below that of the rated technical capacity of the unit.
b.	Flexibility.—Portable and mobile laboratories may have darkrooms designed for developing and printing in a single unit, or separate units may be required for different types of darkroom work. Portable and mobile laboratories permit flexibility in the size of the photographic organization inasmuch as additional units may be assigned or attached to the original laboratory. However, because of the compact arrangement of the darkrooms of a portable or a mobile laboratory, it is always advisable to utilize additional working space. This space may be secured by using paulins adjacent to the portable and mobile laboratories, by tentage, by existing buildings, or by temporary construction to provide protection against wind and weather. The amount of space needed depends upon the size of the photographic organization and the type of work being performed; that is, a unit engaged in mosaic assembly needs more illuminated workroom space than one whose mission requires only the delivery of unmounted prints.
c.	Preparation for movement.—Commanders of portable and mobile laboratories must be familiar with the shipping dimensions of their equipment and its total weight. In case of water shipment, it is essential that the commander know whether the maximum linear and
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cubic dimensions permit shipment below deck in the average transport, or whether it must be carried as a deck load. Units will be trained to prepare rapidly for movement and also to go rapidly into photographic production upon reaching a destination.
d.	Lighting and power systems.—Electricity for lighting and power in temporary or mobile laboratories should be procured from existing lines to as great an extent as possible. When outside current is not available, the portable generating system provided for field use must be employed.
e.	Water systems.—All mobile laboratories are equipped with water pumps. Flexible hose is provided for connection of the pumps with a nearby water pipe, well, stream, or other water source. Each unit also is equipped with a water tank which supplies the faucets. Collapsible water tanks are carried for use in tents and temporary laboratories.
396.	Procurement of equipment and supplies.—Current supply regulations prescribe the manner of obtaining equipment and supplies. Materiel is obtained by requisition or by local purchase.
397.	Loan of equipment.—The loan of Government property for private use is prohibited. The equipment issued a photographic unit is to enable it and related flying units to discharge their functions. As the proper use of this equipment is only in the performance of such functions, the personnel assigned to discharge them should be the only persons allowed to use such equipment.
398.	Records.—Current regulations prescribe the materiel reports that should be made and records to be retained in the photographic unit. Regulations advocate the use of a bin card or form of perpetual inventory for expendable photographic supplies. This should balance at all times, but irrespective of the present or any future system of account for supplies, the laboratory commander must always be able to determine instantly the quantity of supplies on hand and must know the extent to which the laboratory can operate. Air Corps Circular No. 15—81 prescribes the manner of obtaining expendable supplies from local agencies. The maintenance of consumption records within darkroom subdivisions is impracticable.
Section III
OPERATION
Paragraph
Authority for photographic work or projects______________________________ 399
Training--------------------------------------------------------------------
Distribution of products____________________________________________________
System of handling______________________________________________
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Paragraph
Standard methods________________________________________________________  403
Allocation of personnel___________________________________________________404
Photographic files________________________________________________________405
Handling films and negatives______________________________________________406
Locations of laboratory sections__________________________________________407
Chemical mixing section___________________________________________________408
Ventilation_____________________________________________________________  409
Camera repair_____________________________________________________________410
Alterations of equipment--------------------------------------------------411
Storage of chemicals______________________________________________________412
Experiment within the laboratory__________________________________________413
Service test equipment____________________________________________________414
Care of equipment_________________________________________________________415
Water and electricity_____________________________________________________416
Storage of inflammable liquids____________________________________________417
Laboratory fire exits, darkroom exit signs, and electric fixtures and
restrictions___________________________________________________________418
Fire extinguishers________________________________________________________419
399.	Authority for photographic work or projects.—The laboratory will engage in those phases of photography as directed by the tactical commander. The allotment of photographic materials to a photographic unit is in an amount sufficient for the training requirements of the unit and of the Air Corps organization to which the unit is attached or with which it is associated. Extensive photographic projects, therefore, which require the use of material in quantities greater than the amount allotted for training purposes, will be undertaken only when directed by higher authority.
400.	Training.—a. By far the most important work done by the photographic unit during peacetime is training in the practice of photography. Work should be so performed that personnel will obtain individual experience of a kind that will prove valuable during military operations, and as far as the quantity of the particular work will extend, exercise in the teamwork that is so necessary during war. Individual technical efficiency should be developed to a high degree, but unit efficiency is paramount. Therefore, the training of the unit must be balanced in all sections and in the various types of missions which the unit may be expected to perform.
b. Practice will improve the quality of the product and the teamwork efficiency of the unit. The laboratory commander should endeavor to maintain an even flow of the various types of missions into the unit in order to maintain unit and individual proficiency with equipment and technique. Army Regulations and technical instructions contain standing orders for many types of photographic mis
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sions. These may be supplemented by the laboratory commander whenever required for individual or unit training.
401.	Distribution of products.—Photographs will be distributed in accordance with the order authorizing their production.
a.	Photography in connection with public relations is subject to the provisions of AR 600-700 and special instructions published from time to time.
ft. Regulations classifying and governing restricted photographs are contained in AR 350-5. The unit commander will individually supervise whenever prints or other products are made from negatives of secret or confidential nature. Only the required number will be produced, and the prints or other products will be properly safeguarded during finishing. Negatives and all prints therefrom will be disposed of immediately, in accordance with orders of competent authority.
c.	Air Corps Circular No. 95—4 requires that examples of photography be submitted semiannually to the materiel division.
d.	The Chief of the Air Corps requires photographs of general service and public interest to be submitted monthly.
e.	Official photographs made in a photo unit by military personnel using Government materiel and supplies are property of the United States. The selling of such photographs, negatives, or any photographic products therefrom, or their distribution in any manner except through regular channels, is prohibited. This prohibition extends to photographs of any kind which photographic personnel have been directed to make for training purposes.
f.	All photographs distributed by the Air Corps will be marked or stamped on the back: “Official Photograph—Published only with the permission of the Chief of the Air Corps.” All copyright privileges concerning any official photograph are expressly reserved by the War Department. No person will be authorized to copyright any official photograph.
g.	Photographs released for publication by proper authority will contain a credit line to read as follows: “Official Photograph, U. S. Army Air Corps.”
h.	In preparing photographic prints, enlargements, negatives, lantern slides, and any other photographic products for shipment by mail, express, or otherwise, care must be taken that proper provisions are made for their protection against damage in transit. Ordinarily, prints, negatives, and lantern slides should be packed in reinforced pasteboard box containers wrapped with paper. Large prints should be packed flat between heavy cardboard when practicable. When
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such prints are shipped in mailing tubes, they should be rolled with the image side out. This will prevent excessive curling when the photographs are removed from the container. Each package of photographs should have on the outside the address of the consignor. Each package or roll of photographs mailed under penalty label should contain a copy of either the original order, a letter of transmittal, or a reference thereto.
402.	System of handling.—a. The routine procedure in handling work must be systematic. The sequence of operations required in production should be performed as efficiently and economically as in any properly managed shop, and the laboratory commander should always be on the alert to improve the system or technique whenever it is apparent a reduction in labor or materials will result.
b. The workrooms must be logically and conveniently located with reference to one another, and within them the apparatus must be properly placed. Failure to observe these elementary principles governing proper organization and arrangement of facilities causes a great loss of efficiency, apparent from the confusion resulting from the movements in the same place of a number of men, each with different tasks, and from the unnecessary walking around necessitated by the inconvenient location of workrooms and apparatus. In making arrangements that will eliminate such unsatisfactory conditions, the requirements of quantity production should be visualized, and the ideal physical plant should locate workrooms, apparatus, and men in a manner that will produce a steady flow of work that can be accomplished with minimum time and effort. In order to do the work required during military operations, the movements of a man in performing a single work operation must be studied with the view of changing or eliminating some of them in order to economize his time and energy. The production of a photograph should be organized along the principle of “line production” in which each workman performs the minimum variety of operations, but the maximum number, in order that the output attain the peak in quantity and quality.
403.	Standard methods.—Laboratory maintenance processes and methods must be standardized to prevent confusion, to economize time and material, and to maintain or improve quality of workmanship. Laboratory rules and regulations should be published covering cleanliness and orderliness, section or room arrangement, use of water and lights, breakage and replacement, labeling of chemicals and sensitized material, handling of chemical solutions and partly
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used boxes of papers and films, handling of negatives, general care of equipment, and establishing definite laboratory inspection periods.
404.	Allocation of personnel.—a. Personnel duty assignments to definite rooms or sections within the laboratory build morale. A chart bearing names of personnel and illustrating relationship of their work to that of the laboratory as a whole assists in creating teamwork, tends to maintain efficiency during frequent periods of personnel exchange and substitution, reduces friction, and establishes responsibility.
Z>. Personnel assignments should result in a proper distribution of the functions of the sections among the personnel, both with regard to individual special qualifications and relative numerical requirements, based on amount of personnel assigned or available to the laboratory. Maximum teamwork can be obtained only when each subdivision has assigned to it men with special aptitudes in quantity to handle exactly the amount of work required of that section, and is provided with an even flow of work involving all the phases of photography for which that section of the laboratory is designated and equipped.
c. The laboratory chief, file clerk, chief film processor, chief printer, and supply clerk should have the status of noncommissioned officers. Administrative duties can be dispatched by a junior clerk under proper supervision.
d. The laboratory chief will normally be the senior enlisted man present. He will assist in general supervision of the plant, materiel, production, and personnel, and enforce the routine procedure and system prescribed by the laboratory commander. He should anticipate supply and personnel requirements, and in general, facilitate teamwork and undelayed production. He should emphasize and augment section responsibility to the end that the loss of personnel within sections shall not be unduly felt in the laboratory as a whole. Individual work assignments should be avoided in favor of section assignments. Production requirements should be clearly understood by all personnel in a section, though responsibility in the section is vested in the senior section man.
405. Photographic files.—a. General.—The photographic files section and its subdivision, production records, is the connecting link between sectional functions in the laboratory subdivisions. Photographic files and records function more smoothly and are better maintained if kept separate from unit administration, even though small or newly formed laboratories utilize the same personnel for the two sections. The field desk accommodations allotted unit ad
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ministration are insufficient to contain the specialized and comprehensive records common to photographic production. Also, it is not customary or desirable to move photographic files and related production records with the unit for either temporary or permanent change of station, provided that photographic facilities will remain in some form to serve local requirements. It is usually inimical to production to place administrative personnel in supervision of files and production records, and this material impedes the prompt discharge of administrative function incidental to change of bases.
b. Types.—Laboratory units administer two types of photographic negative files and records.
(1) General.—The general or miscellaneous files contain both ground and aerial negatives and the correspondence relating to them. These files accumulate incidental to routine production orders which the usual quantity of training supplies builds up, and they do not require a redistribution of personnel or an increase of working hours as they will engage personnel for only brief intermittent periods.
(&) Work orders.—To facilitate general or miscellaneous production, a suitable work order blank form should be adopted by the laboratory. The following entries will be made on this form: Date initiated, serial number of work order, consignee, production specifications, negative file numbers, production accomplished, cost statement (if required), distribution authentication, and monthly production entry.
(&) Monthly production record.—N blank form adapted to the entry of individual work order numbers, subject reference, and monthly recapitulation of work order production figures should be adopted and used. Completed work orders may be filed after entry on the monthly production record, which may be filed after assisting in the rendition of the Training and Operations Report required by Air Corps Circular No. 15-10.
(2) Projects.—Size and requirement of cost reimbursement determine whether an approved photographic request is termed a project. Some Air Corps photographic missions are extensive and require project handling, but usually projects are cooperative work with other branches of the War Department or Federal agencies. It is important to recognize a project as such in its initial stages and organize for it during the period when adequate flight and plot maps, materiel specifications, and priorities are being formulated or received and estimates are compiled. These requirements overburden a normal photographic files section and it is under these circumstances that the normally atrophied production records section is
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reinforced substantially. This can best be accomplished with additional personnel in the files section at the expense of darkrooms or other sections. These men should undertake the more mechanical work of titling films and compiling index maps under the close direction of the files clerk who should individually prepare project folders for the inclusion of the project basic authority, all specifications, original plot maps, correspondence, letters of transmittal and acknowledgment, completed project work orders, and production costs. A project folder is prepared for each project in the laboratory and totals of production records therein are transferred to the monthly production record for inclusion in the Training and Operations Report.
Because of the continuity of work and similarity of specifications, project production is relatively simple in the darkrooms, but because of volume, irregularity in negative titling, and unusual correspondence requirements, the files section is best served by a sharply delineated production records section which is handled by the chief file clerk. This section assumes the proportions necessary to the project; that is, supervising files and obtaining special titling and storage, maintaining priorities as established by the tactical commander, and limiting miscellaneous work during the period. It is charged with ascertaining and maintaining specifications; estimating time, cost, and special supply requirements; progressive cost compilation; supervision of negative titling; plotting and index map reproduction; project work order initiation; verification of products; distribution authentication; correspondence; project report preparation and the possession by the unit of a complete file of records at completion of the project. Although the production records section is always active, its duties are normally so slight that its function is not emphasized in the files section. At the close of a project, production records assumes this position, at which time the minor records incidental to general or miscellaneous production are resumed by the files section.
(a) Project work order.—Project production can be greatly facilitated by the use of a special 'work order blank form. Frequently, when the size of the project justifies, the blank form may include those specifications not subject to change. As a rule, processing instructions are consistent on all related orders and can therefore be brief, though exact, with reference to papers and amounts. Unusual and adequate space should be allotted that part of the form listing the
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file numbers of negatives covering the flight lines which are the subject of the camera exposure record. The form should accommodate flight line reference and establish the roll and negative numbers pertaining thereto. The form should include date initiated, roll number, project name and number, specifications, negative file numbers by strips, production accomplished, cost statement (if not otherwise provided for), distribution authentication, and monthly production entry. The completed project work order should be filed with the project records.
(&) Cost estimates, records, and reports.—The laboratory is customarily required to estimate project costs, under function subdivisions, prior to approval of the project and its final specifications; cost estimates are required in every case involving cost reimbursement prior to engaging the project. Specifications must be closely observed and considered with regard to plant, equipment, personnel, supplies, and priorities before statements regarding cooperative projects are submitted. Frequently the project, as specified, is impracticable with the equipment possessed, will prevent all other training gained from miscellaneous photography, and will require the use of supplies not standard in the Air Corps. Specifications unsuited to equipment should be taken exception to and the cooperative agency must be required to furnish direct to laboratory stocks not standard. Wastes in connection with projects through the employment of inexpert personnel are properly chargeable to training, but cognizance of these discards must be taken in estimates, and where special papers and supplies are furnished by the cooperative agency, must be borne by the cooperative agency. In the photography of forested and unmapped areas where much plotting is verified by print assembly not otherwise required, as much as 25 percent of the printing costs are production waste insofar as delivery is concerned. Special laboratory cost recapitulation blank forms may be originated, if desired, but the practice is generally discouraged because suitable work order forms make it unnecessary from the viewpoint of the laboratory. The expenses of flight personnel and equipment are, within specifications and regulations, chargeable to the project cost but their maintenance and compilation are the responsibility of flight personnel. Projects involving cost reimbursement usually require cost reports at the end of the fiscal year and a complete report on the project is required at the completion of the project. This report is made by the tactical commander and requires the rendition of reports to him from all units
298620°—41----19
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involved. Chemical costs are the most difficult to ascertain since project work is accomplished in conjunction with other wTork, and it is impracticable to distinguish between the two in darkroom procedure. It is most practical to ascertain the number of prints or the number of negatives that may be processed in a given amount of chemical solution, then ascertain the unit cost of the various solutions and compute for total production. The use of a cost form such as shown below, will assist the preparation of original cost estimates, emphasize the items which are properly the subject of cost record maintenance, and materially contribute to the formation of final cost reports.
PROJECT COST CARD
Project name and number_____________ Completion date_________
SPECIFICATIONS: Include altitude flown, scale of negatives, map scale furnished, camera type, overlap each way, area by name, number of prints, size and type, to whom delivered, etc.
Exposures made	Negatives used________ Prints forwarded_______
Flying time----hrs.____mins. Prints forwarded by size .	___ _______ _
Area by square miles _	_	Prints forwarded by size______ _________
Cost per square mile $-------- Prints forwarded by size_______ _________
Aircraft costs:	A. C.
Oil (qts.PH)_____for____(hrs.) (total)__@_____$________
Gas (gal.PH)_____for____(hrs.) (total)__@_____£ $_ _
Grease (kind)_____________(amt.)________@_____f
Total cost
Miscellaneous costs:
Telegrams___________________________
Hangar rentals______________________
Parcel post_________________________
Bills of lading_____________________
Local repairs, facilities, incidentals. _ Film costs:
------rls 9%" by 75' @ $.
______rls 6" by 120' @ $.
------rls 7" by 12' 3" @ $ ------shts 8" by 10" ------shts 20" by 24" @$
Dept. Total $______
$_____
$_____
$_____ $_________
______ $_____
$_____
$_____
$_____ $_________
Dept. $______
$_____
$_____
$_____
$_____
Total cost Total cost Total cost Total cost Total cost
A. C.

Total costs $____
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A. C. Dept.	Paper costs		
	 	gr (type)	(size)	@ $___	-	— $	
	 	gr (type)	(size)	@ $___	__	— $	
	 	gr (type)	(size)	@ $___	__	— $	
	 	gr (type)	(size)	@ $___	__	— $	
	 	gr (type)	(size)	@	__	___ $	
	 	gr (type)	(size)	@	-	$	
	 	gr (type)	(size)	@	__	— $	
	 	gr (type)	(size)	—	__	--- $	
Chemical costs		Air Corps
	tanks (3 gal.) developer (film) @		__	--- $	
	tanks (— gal.) developer (film) @		__	--- $	
	tanks (20 gal.) developer (film) @		__	___ $	
	tanks (25 gal.) developer (film) @		__	$	
	gallons developer (film) @		__	-- $	
	gallons developer (film) @		__	--- $	
	gallons developer (paper) see note @		__	$	
	tanks (3 gal.) fixing bath (film) @		__	— $	
	tanks (—gal.) fixing bath (film) @		__	-- $	
	tanks (20 gal.) fixing bath (film) @		__	$	
	tanks (25 gal.) fixing bath (film) @			___ $	
	gallons fixing bath (film) @		__	— $	
	gallons fixing bath (paper) see note @—	__	-- $	
	Total cost $	 $			
	Total project cost $		
Chemical figure basis:	Reimbursement to Air Corps $--------
Per qt. developer: 60 8 x 10; 15 16 x 20; 10 20 x 24.
Per gal. fixing bath: 50 8 x 10; 12 16 x 20; 8 20 x 24.
c. Duties and responsibilities.— (1) All production and training should be covered by work orders initiated by files. Work required by custom or competent authority to be undertaken instantly must be reported promptly to the files section for initiation of laboratory work order. Verbal requirements will always be followed by initiation of laboratory work orders, which should be accomplished by the closely supervised files section rather than by an individual. An entry of each work order initiated will be maintained in the files section on the monthly production record, and after accompanying the material through the various sections, production entries will be made after completion and the order filed under monthly records.
(2)	The files section is charged with titling and the storage of recorded and titled negatives. Untitled negatives do not form a part of negative files and retention of such material should not be
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required. Files must accomplish the plotting of negatives and initiate the reproduction of index maps to accompany photographic products. Immediate steps must be taken to obtain and insert in negative roll cans index map reproductions of suitable scale which will identify the negatives. Every can must contain an index map.
(3)	Files are charged with ascertaining knowledge of and furnishing information relative to the status of uncompleted work. Decisions involving priorities are coordinated and executed through the files section which must know the obligations of the laboratory and the state of current production. The laboratory commander and laboratory chief must support the supervision contemplated above or the system will be impaired to the extent that satisfactory production will be accomplished only when the material is personally conducted by them through the laboratory. This cannot be the case because the commander has administrative duties and his chief laboratory technician must devote much of his time to darkroom production quality, teamwork, plant maintenance, repair, and personnel and operating problems.
(4)	The files section should verify the quantity and quality of production preliminary to distribution.
(5)	Files must effect or authenticate distribution.
(6)	Air Corps Circular No. 95-3 governs the titling and identification legend to be used on all negatives. A loose-leaf file book should be maintained for negative files, listing each negative, adequately supported by subject cross-reference index cards. Photographic units are authorized an Air Corps 14-inch typewriter for photographic files and production records and reports.
(7)	Flight and laboratory personnel must cooperate in the composition of a complete cameraman’s exposure log which supplies all the information required by the tactical commander, processing sections, and titling requisites of photographic files. This log must be delivered to the laboratory with exposed films.
(8)	Film identification is the responsibility of the camera operator and must be satisfactorily accomplished prior to film delivery. Tolerance of other identification means will result in the dumping of partially unidentified films into the files section, the initiation of unspecific work orders, and the partial identification with the aid of verbal description. In this case, identification has been made by the files section and it is the repository of remaining untitled negatives incapable of being filed and about which there is hesitation to
TM 1-219
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discard. The laboratory commander should avoid the acceptance of unidentified films unless untitled production is required in emergency.
(9)	Photographic files are further charged with the compilation and maintenance of all records and correspondence relating to photography and the preparation of reports thereon. Competent assistance may be required.
406. Handling films and negatives.—a. Proper and methodical arrangements for the accommodation of films and negatives must be made from the time of arrival of exposed films in laboratory to final disposition of negatives. This is essential to prompt and orderly production and the reduction of fire hazards.
ft. Films should arrive in processing sections accompanied with work orders containing instructions relative to processing and priority. Information on the work order must include date and hour of exposure, subject or type of mission or both, altitude and weather conditions, filter, shutter speed, aperture, camera and magazine numbers, and exact number of exposures. The film following the last exposure should, in the case of roll film, be marked with the work order number assigned and after processing be respooled and delivered in the can with the work order bearing appropriate production entry to photographic files section. Cut films usually are in small quantities and are identifiable with the subjects of the camera operator’s log. After processing, they should be placed in preservers in the order of subject listing and delivered with the work order to files section. In the files section, the negatives remain in a receptacle labeled “awaiting titling.” After preparation for further production, which may involve discard of negatives and part rolls, they are placed in a receptacle marked “awaiting production,” the work order now containing negative numbers and further processing instructions and the whole material so located in the receptacle that priority of further processing is indicated. It should be customary for the chief printer to visit this section hourly and scan the orders taking the first for production as printing progress permits or when priority demands. Printing orders customarily are delivered to the finishing section after darkroom work is completed, and in the cases of small orders on cut films, the films remain with the work orders and are delivered with prints to files. Roll films must always be returned direct to the files section and placed in the receptacle marked “completion.” All other negatives, their prints and the work
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orders are delivered to this receptacle by the printing chief who supervises the finishing section.
c.	Unless essential, the partition of rolls should be avoided. Roll use is the safest and most expeditious manner of handling negatives from exposure to final storage discard. Rolls must always be kept in cans when not the subject of immediate use.
d.	Field operations involving the handling and processing of films may differ materially from the normally accepted methods. Those work orders whose first requirement is speed in delivery usually involve only small parts of rolls or single exposures. Several exposures may be developed in about 3 minutes, rolls and part rolls in about 5 to 6 minutes. After the emulsion has cleared in fixation bath, single exposures and strips of about three exposures may be placed, base down, upon ferrotype plates and the surface water on the emulsion swabbed by damp chamois or squeegeed off with print squeegee or other flexible rubber wiper without practical injury to the negatives. Soaking for 2 minutes in an ethyl alcohol bath, followed by airing in heated or dry room or facility for 1 or 2 minutes, produces negatives sufficiently dry for printing. Methyl alcohol should not be used because it will attack a film support. It may be necessary to refix and wash these negatives later, though usually this is impracticable. Negatives apart from full rolls may be given normal handling in chemical baths and then be cut, washed, and dried individually or in short strips, with the dispatch indicated, and commensurate with the ability of other sections to handle further production of the order. Night processing for morning delivery is customary and drying in portable facilities involves the intelligent use of any heated or otherwise desirable facility. Frequently films may be strung across the ceilings or nearby structures, however poorly adapted to use, and drying hastened by the use of alcohol, gasoline, or kerosene stoves or pots from a safe distance below. A full use of cook tents has been made in the past where prior hot fires have produced a pocket of warm, dry, upper air. Any expedient capable of hastening the drying of films in poor accommodations must be utilized to the extent consistent with common sense safety factors.
e.	Acetate base films are brittle when dry and in dry climates or well-heated interiors they shatter or break readily. When allowed to peel from the roll as a ribbon of considerable length, tearing invariably occurs. These negatives are required to be wound on spools,
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emulsion out, and it is important that the first spooling be accomplished in this manner since much of the excess drying occurs immediately after processing and the shape assumed by the negative base at that time will persist throughout the life of the negative. Original excess drying can be avoided on forced air dryers, but when recourse is had to free air afforded by slotted wheels or makeshifts, the negatives should not be left overnight and must be spooled immediately after they are sufficiently dry to prevent adhesion.
f.	Film discards and scraps constitute a fire hazard, a subject treated in AR 850-65. Strict adherence to smoking prohibitions and the designation of one closed waste receptacle for all film discards will reduce film fire hazards.
g.	AR 850-65 and Technical Order No. 10-5-1 prescribe proper storage facilities and precautions.
h.	Negative files accumulate quickly and untitled negatives in storage are not tolerated. Laboratory commanders should insist that the requirements of film identification be met. Initiative must be exercised in the transfer or destruction of negatives of questionable value to the unit by representations made to the tactical commander and, when necessary, through him to interested agencies.
407. Locations of laboratory sections.—Essential teamwork within the laboratory depends largely upon plant lay-out. Even in the more or less complete mobile units where section location is predetermined, there is a tendency to develop auxiliary accommodations which are frequently essential to required production. This addition, the construction or enlargement of portable laboratories and the utilization of permanent laboratories, should be such as to facilitate the exchange of information and materials in the course of production.
a.	Administration and supply are closely correlated in the photographic unit. In small units and particularly in the field where intense personnel utilization is necessary to production requirements and plant restrictions, they are advantageously housed together while their joint location within the laboratory is relatively unimportant.
b.	Print finishing is usually final production. Where possible, it should be accomplished under controlled atmospheric conditions and adequate illumination. Whatever the plant accommodations, vigorous action should be taken to create a housed weather and wind protected finishing section, as wind, dust, and dirt defeat print finishing quality and the orderly assembly of print orders. All printing darkrooms are best located within a single block, the center of which is
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occupied by the finishing section and the print passage which is facilitated by the use of wall light traps rather than doors equipped with light traps or curtains that delay or hamper ready tray passage.
c.	Photographic files should be located directly opposite or contiguous to the finishing section. Files must know currently the progress of orders through the printing and finishing sections and every effort should be made to facilitate this intercourse. Field operation requires the closest contact between these sections and limited housing frequently results in dual use of existing facilities.
d.	The creation of an adequate negative processing section in a portable laboratory is the first consideration of the laboratory personnel. The negative processing section requires no special location within the unit, though proximity to the files section is advantageous to both.
408.	Chemical mixing section.—a. Chemical solutions should be prepared in a well-ventilated room unrelated to the storage or processing of sensitized materials. A weighing table, equipped with suitable scales, should adjoin a sink of generous dimension for the actual mixing. A series of formula cards should be employed in card index form and the formulas, while conforming to the proportions furnished in appendix I, should be computed in the largest amount of solutions consistent with the needs of the laboratory in order to minimize human error in weighing under adverse conditions. The cards should be dated and initialed by the individual responsible for the quality of chemical solutions within the laboratory in all cases where the specifications differ from the basic formula in any respect, including simple increase or decrease in volume. The use of special and nonstandard solutions create confusion and lack of confidence and responsibility in the laboratory and do not contribute to quality work. The feasibility of the use of only one formula in varying strengths for all standard processing of sensitized materials has been well established. This practice should be quickly adopted in time of emergency or for field operation.
b. The film processing section has the prime need of faultless chemical solutions; therefore, chemical mixing is treated as a subdivision of that section and selected men should be rotated to relieve tedium under the supervision of the individual responsible for film processing.
409.	Ventilation.—Adequate ventilation of laboratories is necessary for the comfort and health of the workmen. A good ventilating system is installed in the mobile laboratories and proper ventilation
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must always be provided in other laboratories. When it becomes necessary to use a poorly ventilated space, the men should be divided into reliefs and observe a schedule which will allow frequent respites and access to the fresh air outside. Care must be taken in building light traps that a sufficiently free passage is left for air.
410.	Camera repair.—a. The supply section is charged with the custody, maintenance, and repair of cameras in small laboratories and during field operations of all photographic laboratories. Extensive laboratories and those housed in permanent buildings usually facilitate equipment repair by the creation of a camera section having only nominal connection with the supply section. It is treated as a part of production and possesses equipment in the same sense that darkrooms are equipped for operation. Such a camera section is charged with custody, issue, maintenance, and repair of all cameras, and such camera mission preparation as is desirable. It may be required to accomplish the repair of all cameras and such camera mission preparation as is desirable. It may be required to accomplish the repair and servicing of all equipment within the limitations imposed by Technical Orders covering equipment.
b.	Routine maintenance of equipment is best accomplished by the adoption and use of equipment cards which provide information required to institute unsatisfactory reports and condense instructions for maintenance or servicing required by Technical Orders. This, or a similar card, should be maintained for individual items of equipment employing gearing or electric motors, such as print wringers and contact printers and other major items having working parts subject to replacement. The cards should be assembled according to the inspection period to which assigned; for example, all printers may be designated for service on the 5th and 20th day of each month, print washers and wringers on the 6th and 21st. The back of the card should be ruled off to form columns under date for the initials of the workman performing the required inspection, oil, greasing, service, and overhaul.
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PHOTOGRAPHIC EQUIPMENT MAINTENANCE RECORD
Name-------------------------------- Type___________ Technical Order_______
Date received----------- Purchase order No______ Located___________________
Contractor-------------------------------------- Contractor’s model No_____
Electric motor numbers------------------- and________________ H. P_________
Periodic service required__________________________________________________
Oiling instructions________________________________________________________
Greasing instructions------------------------------------------------------
Inspection period to which assigned________________________________________
Was unit received new____________in good condition_________________________
Date installed_______________ Is machine being used________________________
Remarks____________________________________________________________________
(If parts have been removed from this machine, their disposition and necessity for such action must be shown under “Remarks”)
SEE BACK OF CARD FOR RECORD OF SERVICE.
c.	Only such repairs or adjustments of cameras or laboratory apparatus will be made in the photographic unit as in the judgment of the unit commander can be undertaken with safety or without damage to the equipment. Extensive repair to cameras and laboratory equipment will not be attempted in the photographic unit. Cameras and equipment will be returned to the base supply.
d.	Air Corps Circular No. 15-45 requires the maintenance of a Camera Inspection Record for each aircraft camera.
411.	Alterations of equipment.—Equipment will be altered only when so ordered by higher authority. Such changes are usually directed by Technical Orders or Technical Radiograms. Equipment will be repaired as indicated in the appropriate Technical Order.
412.	Storage of chemicals.—Photographic chemicals are stored in accordance with Technical Order No. 24-1-1.
413.	Experiment within the laboratory.—Prolonged test and experiment is not the function of a service unit and is detrimental to the efficiency of the laboratory. Only those relatively simple and brief tests will be made that are necessary to the rendition of intelligent and comprehensive unsatisfactory reports.
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414.	Service test equipment.—New types of equipment are usually given thorough tests by field units before general adoption and distribution in the Air Corps. Sometimes photographic units will be called upon to make practical tests of the new types of photographic equipment. Before undertaking such tests, thorough instruction should be received in the use of the equipment, the tests should be full, fair, and impartial as possible, and the recommendations made should be consistent with the best interests of the military service.
415.	Care of equipment.—The production of satisfactory work by a photographic unit is to a large extent dependent upon the working conditions of its equipment. Frequent tests and inspections should be made of equipment by the unit commander for the purpose of ascertaining its operating efficiency, and particularly whether the detailed instructions that should have been previously issued by him governing its use are being strictly observed by the personnel of the unit. Prompt and appropriate disciplinary action should be taken in any case of neglect or abuse of equipment or disregard of orders or instructions concerning it. Any inherent defects in equipment because of poor design or defect in manufacture should be made the subject of an unsatisfactory report.
416.	Water and electricity.—Modern photography is completely dependent on water and electricity.
a.	Base field laboratories require adequate quantities of water under pressure. Any water system serving human needs and consumption may be presumed to be satisfactory for photographic purposes, though frequent filtering will be necessary. It is preferable to maintain a laboratory only where adequate water is available rather than undertake the correction of a deficiency. Mobile and advanced laboratories are equipped to function from local water systems, from streams or ponds nearby, or by the use of auxiliary mobile water tanks. These laboratories can operate successfully on most clear waters and roily waters are relatively satisfactory after filtering. Waters with sufficient chemical taint to preclude ready use should be avoided by advanced field laboratories.
b.	Base field laboratories are always located where adequate outside electric current is available. Foresight must be exercised in estimating current requirements, and line capacity to the various laboratory sections must be given fullest consideration to prevent line overload during periods where considerable electric equipment is in simultaneous operation. Mobile laboratories are equipped with power source and wiring closely calculated for estimated requirements. Additional light and power outlets, often desirable under exigencies, should be made only
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after line capacity and power source have been augmented or determined to be sufficient for the contemplated extension. Every effort should be made to obtain electric supply from outside source in every circumstance, since it is more dependable and less limited.
417.	Storage of inflammable liquids.—Inflammable liquids in use in the laboratory should be held to absolute minimum at all times and storage facilities for partly used or unsealed containers should be maintained at a distance from the laboratory. Technical Order No. 10-5-1 refers to such storage.
418.	Laboratory fire exits, darkroom exit signs, and electric fixtures and restrictions.—AR 850-65 covers the marking of exits and exit sign specifications and prescribes electric circuits and fixtures used in connection with certain phases of film processing.
419.	Fire extinguishers.—a. Soda and acid.—(1) Soda and acid fire extinguishers contain chemicals for generating carbon dioxide rapidly, as by mixing sulfuric acid with a solution of sodium bicarbonate when the apparatus is inverted. Water is the extinguishing agent. The pressure exerted by gas forces a stream of water on the fire. This appliance is effective on incipient fires in ordinary burning materials such as wood, paper, textiles, rubbish, or a combination of these materials where the quenching and cooling effect of quantities of water is of the first importance.
(2)	To operate, turn upside down. Direct the stream at the base of the flames. Follow the flames with the stream.
Caution: Do not use on electricity, gasoline, or any other liquid that is lighter than water.
b.	Foam.—(1) The basis of the foam system of fire extinguishing is the use of chemicals that combine to create a large volume of carbon dioxide gas confined in tough, durable bubbles of foam easily applied and readily adhering to any burning surface. The mixture spreads out as a blanket, smothering the fire. It is most effective on oil fires. In ordinary burning materials, the foam may be used to coat the surface of the burning area, as a blanket. It does not penetrate so well as water.
(2)	To operate, turn upside down. The stream should be directed against the inside of the opposite wall of the tank above the burning liquid so as not to splash fire. Walk around the fire if possible. If the fire is on the floor, stand back and allow the foam to fall on the fire without much force, preventing the spread of flames.
Caution: Do not use on electricity.
c.	Carbon tetrachloride.—(1) When a stream of this liquid is directed against a burning surface, the heat causes it to evaporate in-
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stantly, forming a heavy gas that displaces the air in contact with the burning material. It is a nonconductor of electricity and may be used on all types of material fires except photographic films and similar plastics. Rooms, closets, or confined spaces should be ventilated immediately after using the extinguisher.
(2)	To operate, turn black wheel on the back of the extinguisher. Direct the stream at the base of the flames and work around the fire rapidly. If the fire is in a container or tank, direct the stream against the inside opposite wall above the level of the burning liquid.
Caution: Do not use on photographic films as the toxic phosgene is liberated.
d.	Carbon dioxide.— (1) This extinguisher may be used for films, alcohol, gasoline, oil, paint, varnish, paraffin, lacquer, inflammable chemicals and liquids.
(2) To operate, pull lock pin on the top of the extinguisher then turn the valve on top of the extinguisher as indicated by the arrow on top of the valve. This will discharge the gas in the extinguisher. Direct the discharge as close to the fire as possible, applying first to the edge and at the bottom of the fire, and progressing forward and upward. Move the discharge horn slowly from side to side. Continue the discharge even after the fire has been extinguished to cool the liquid and prevent possible reflash.
Caution: Do not turn on extinguisher until in position ready to fight the fire.
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Appendix I
FORMULARY
Paragraph
General__________________________________________________________ 1
Time of development_____________________________________________  2
Developer formulas_______________________________________________ 3
Fixing solutions_________________________________________________ 4
Rinse and stop baths_____________________________________________ 5
Reducing solutions_______________________________________________ 6
Intensification__________________________________________________ 7
Toning----------------------------------------------------------- 8
Miscellaneous formulas___________________________________________ 9
1.	General.—It is quite possible to select one developing formula which will give satisfactory results with many sensitized materials, but certain emulsions definitely require specific formulas to insure optimum results. If a developer is being selected for a particular use, both the sensitized material and the specific type of work to be accomplished should be carefully considered. The recommended procedure in processing is to use the developer which is specified for the particular emulsion. The purpose of this formulary is to furnish the data necessary for mixing and using solutions as to chemicals, quantities, temperature, method of use, dilution, and length of time a material is to be treated.
2.	Time of development.—The developing time as stated in the directions with each developed formula is not intended to be definite for all materials and types of work, but is merely an approximate guide to be used when the correct time is not known. It is impossible to state one developing time for all materials because the photographic image is influenced by many other factors, such as range of brightness in the subject, type of lighting, inherent contrast of material, emulsion speed, and color sensitivity.
3.	Developer formulas.—a. For negative materials.—(1) Normal contrast developers.
{a) Air Corps specification developer.
Stock solution
Water (at 100° F.)____
Metol_________________
Sodium sulfite (des.)_
Hydroquinone__________
Sodium carbonate (des.)
Water to make_________
_________ 96 ounces
________ 198 grains
6 ounces, 176 grains _ 1 ounce, 44 grains
7 ounces, 264 grains
___________ 1	gallon
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Dissolve about one-tenth of sulfite, then the remaining chemicals in the order given. For films in tray, use one part of stock solution to four parts of water. Develop 4 to 6 minutes at 65° F. For tank development, dilute one to four. Develop 5)4 to 7)4 minutes with continuous agitation.
(5) ABC pyro developer.
Solution A
Water (at 100° F.)_______________________________________ 1	gallon
Potassium metabisulfite_______________________1_______ 4 ounces
Metol---------------------------------------------------- 4	ounces
Pyro (crystals)__________________________________________ 4	ounces
Potassium bromide______________________________________ 220	grains
Dissolve about one-half the metabisulfite and then the metol. Dissolve the remainder of the metabisulfite, then the pyro, and last the bromide.
Solution B
Water (at 100° F.)_______________________________________ 1	gallon
Sodium sulfite (des.)___________________________________ 14	ounces
Solution C
Water (at 120° F.)_______________________________________ 1	gallon
Sodium carbonate________________________________________ 10	ounces
For use, dissolve one part of each solution in six parts of water. Develop 6 to 9 minutes in tray at 65° F.
(c) Metol-hydroquinone-borax developer (for maximum shadow detail).
Water (about 125° F.)_____________________________
Metol_____________________________________________
Sodium sulfite (des.)_________________ _13 ounces,
Hydroquinone______________________________________
Borax, granular___________________________________
Water to make_____________________________________
96 ounces
106 grains
110 grains
290 grains
116 grains
1 gallon
Dissolve chemicals in the order given. Use without dilution. Average development time about 20 minutes in tank at 65° F. or about 12 to 15 minutes in tray.
(<7) Metoldiy dr o quinone developer (for all types of films).
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Stock solution
(about 125° F.)___________________________ 64
Metol__________________________________________ 180
Sodium sulfite (des.)____________________________ 6
Hydroquinone_____________________________1 ounce, 260
Sodium carbonate (des.)__________________________ 9
Potassium bromide______________________________ 108
Water to make____________________________________ 1
ounces grains ounces grains ounces grains gallon
Dilute one part stock solution to 4 parts water. Develop films 4 to 6 minutes at 65° F. in tray.
() For tray or tank use.
Water (at 120° F.)_________________________
Metol______________________________________
Sodium sulfite (des.)__________________9 ounces,
Hydroquinone___________________________ 1 ounce,
Sodium carbonate (des.)________________6 ounces,
64 ounces 128 grains 265 grains
75 grains 180 grains 240 grains
1 gallon
Potassium bromide__________________________
Water to make______________________________
Dissolve chemicals in the order given, using full strength. Develop about 15 minutes at 65° F. in automatic developing tank.
b. For positive materials.— (1) Specification developer.—Dilute one part stock solution with two parts of water.
Chloride paper_______________________1	to	11/4	minutes	at	65°	F.
Bromide paper________________________2	to	2%	minutes	at	65°	F.
Bromochloride paper__________________2	to	2%	minutes	at	65°	F.
Lantern slides-----------------------2	to	3	minutes	at	65°	F.
(2)	For bromide and bromo chloride papers.
Water (at 120° F.)------------------------------- 64	ounces
Metol____________________________________________ 88	grains
Sodium sulfite (des.)_____________________________ 3	ounces
Hydroquinone------------------------------------ 360	grains
Sodium carbonate (des.)___________________________ 2	ounces
Potassium bromide________________________________ 88	grains
Water to make_____________________________________ 1	gallon
Dissolve chemicals in order given. Dilute 1 to 1. Develop 2 to 3 minutes at 65° F.
(3)	Chloride paper developer (for blue-black tones).
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Stock solution
Water (at 120° F.)_________________________
Metol______________________________________
Sodium sulfite (des.)_________________ 5 ounces,
Hydroquinone___________________________ 1 ounce,
Sodium carbonate (des.)_______________________
Potassium bromide____________________________
Water to make________________________________
64 ounces 160 grains 145 grains 190 grains 10 ounces
48 grains
1 gallon
Dissolve chemicals in order given. Dilute stock solution in two parts of water. Develop 1 minute at 65° F. or 45 seconds at 70° F.
(4)	Lantern slide developer (for warm black tones).
Stock solution A
Water (at 125° F.)________________________________ 64	ounces
Sodium sulfite (des.)____________________________ 360	grains
Hydroquinone------------------:__________________ 400 grains
Potassium bromide-------------------------------- 200	grains
Citric acid--------------------------------------- 40	grains
Cold water to make_________________________________ 1	gallon
Stock solution B
Cold water_________________________________________ 1	gallon
Sodium carbonate (des.)____________________________ 4	ounces
Sodium hydroxide_________________________________ 240	grains
Dissolve chemicals in the order given. For use, take equal parts of A and B. For still wanner tones, take one part of A to two parts of B. Stir thoroughly before use. Develop about 5 minutes at 70° F.
(5)	Lantern slide developer (for cold black tones).—Use specification developer, 1 to 2, for 2 to 3 minutes.
4.	Fixing solutions.—a. Acid hardening fixing bath (for films, plates, papers).
Solution A
Sodium thiosulfate (hypo)____________________________ 2 pounds
Water to make________________________________________ 1 gallon
Dissolve completely. If hydrometer issued, reading should be 68 at 65° F.
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Solution B (hardening bath)
Water (at 125° F.)---------------------------------- 56	ounces
Sodium sulfite (des.)________________________________ 8	ounces
Acetic acid (28 percent)--------------------------- 24 fluid ounces
Potassium alum_______________________________________ 8	ounces
Water to make________________________________________ 1	gallon
Dissolve chemicals in the order given. For use, add one part hardener to six parts plain hypo solution. Fix films, plates, or papers for 15 minutes at 70° F.
b.	Boric acid hardening fixing bath (more stable and better hardening) .
Water (at 125° F.)----------------------------------- 80	ounces
Sodium thiosulfate (hypo)_____________________________ 2	pounds
Sodium sulfite (des.)_______________________________ 2 ounces
Acetic acid (28 percent)______________________________ 6	ounces
Boric acid (crystals)_________________________________ 1	ounce
Potassium alum________________________________________ 2	ounces
Water to make----------------------------------------- 1	gallon
Dissolve chemicals in the order given. Films and plates will fix completely in 10 minutes in fresh bath.
c.	Formalin fixing hardening bath.
Sodium thiosulfate___________________________________ 36	ounces
Sodium sulfite (des.)_____________________7 ounces, 80 grains
Formalin (40 percent formaldehyde)___________________ 17	ounces
Water to make----------------------------------------- 1	gallon
Dissolve chemicals in order given.
d.	Nonhardening firing bath (for paper prints).
Water (at 125° F.)_____________________________________ 64 ounces
Sodium thiosulfate (hypo)______________________________ 2 pounds
Sodium sulfite (des.)________________________ 1 ounce, 140 grains
Sodium bisulfite_____________________________3 ounces, 140 grains
Water to make------------------------------------------ 1 gallon
Dissolve chemicals in order given. Do not use above 65° F. Dry prints slowly.
5. Rinse and stop baths.—(«.) Acetic acid rinse (for papers).
W ater-------------------------------------------- 1 gallon
Acetic acid (28 percent )_________________________ 6 ounces
Rinse prints at least 5 seconds, 65° F.
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b. Acetic acid rinse (for films and plates).
Water---------------------------------------------- 1 gallon
Acetic acid (28 percent)___________________________ 16 ounces
Rinse negative about 5 seconds, 65° F.
c. Tropical hardener rinse (films and plates).
Water_______________________________________________ 1	gallon
Potassium chrome alum_______________________________ 4	ounces
Sodium sulfate (des.)------------------------------- 8	ounces
To be used after brief water rinse if temperature is below 85° F. If above 85° F., omit water rinse. Discard bath when it appears yellowgreen.
6.	Reducing solutions.—a. Subtractive reducer.
Solution A
Water---------------------------------------------- 16 ounces
Potassimum ferricyanide____________________________1% ounces
Solution B
Water---------------------------------------------- 1 gallon
Sodium thiosulfate (hypo)-------------------------- 2 pounds
Add one part A to four parts B; then add water to make 32 parts. Pour solution over negative to be treated. Examine negative frequently during reduction and remove to wash when sufficiently reduced.
b.	Proportional reducer.
Stock solution A
Water----------------------------------------------32	ounces
Potassium permanganate_____________________________ 4	grains
Sulfuric acid (10 percent)-------------------------y2	ounce
Stock solution B
Water----------------------------------------------96	ounces
Ammonium persulfate-------------------------------- 3	ounces
Take one part solution A to three parts solution B. When the negative is sufficiently reduced, clear in 1 percent sodium bisulfite. Wash negative thoroughly before drying.
c.	Superproportional reducer.
Stock solution
Water----------------------------------------------- 1	gallon
Ammonium persulfate_________________________________ 8	ounces
Sulfuric acid, concentrated_________________________ 3	drams
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Dilute one part stock in two parts water. When reducing is complete, immerse negative in acid fixing bath for a few minutes and wash thoroughly. If reduction is too rapid, dilute further.
7.	Intensification—a. Mercuric chloride intensifier.
Bleacher
Water (cool, 60° F. to 70° F.)_________________28	ounces
Potassium bromide-------------------------------%	ounce,	55	grains
Mercuric chloride------------------------------ %	ounce,	55	grains
Water to make----------------------------------32	ounces
After negative is bleached, wash thoroughly and blacken in either of the three solutions given below. These solutions give greater density in the order given.
Solution No. 1
10	percent solution of sodium sulfite. The B solution of ABC developer works satisfactorily.
Solution No. &
One-half tray strength metol hydroquinone developer (specification developer).
Solution No. 3
10 percent solution of ammonia.
b. Chromium intensifier (for professional films and plates).
Stock solution
Water------------------------------------------32 ounces
Potassium bichromate--------------------------- 3 ounces
Hydrochloric acid (C. P.)----------------------2 fluid ounces
For use, take one part stock to 10 parts water. Harden negative with alkaline solution of formalin before intensification to prevent reticulation. Bleach negative thoroughly and wash for 5 minutes. Redevelop fully in a non-staining developer. (Avoid developers with high sulfite content.)
8. Toning (Sepia toning, redeveloping process).
Bleacher
Water (cool, 60° F. to 70° F.)---------------------18	ounces
Potassium ferricyanide_____________________________ 1	ounce
Potassium bromide__________________________________ 1	ounce
Water to make______________________________________24	ounces
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For use, dilute one part of above stock solution to one part water.
Note.—While the above solution may be mixed in the order given, the operation is facilitated by grinding ferricyanide and bromide together, with mortar and pestle, and dissolving in the water.
Redeveloper
Water (at 100° F.)------------------------------------- 12 ounces
Sodium sulfide (not sulfite)___________________________ 1 ounce
For use, one part stock solution to eight parts water.
Note.—Use enamel trays (no metal exposed) for the above two solutions. If blue (or greenish) spots appear on prints it is an indication of iron in water, either from trays or in the ferricyanide itself.
Caution: As the fumes of sodium sulfide are harmful to sensitized emulsions, this chemical should not be mixed or used in a place where the fumes will come into contact with such materials.
9. Miscellaneous formulas.—a. Tray cleaner.
Potassium dichromate (or bichromate)______________________ 16 ounces
Water (cool, 60° F. to 70° F.) to make____________________112 ounces
Sulfuric acid (C. P.)------------------------------------- 16 ounces
Dissolve potassium dichromate and then add sulfuric acid slowly to the solution. Adding the acid too fast will result in overheating.
Caution: Never add water to acid, but add acid to water.
b. Tray cleaner (nitric acid).—For cleaning Allegheny metal trays, buckets, and other containers, use a 25 percent solution of
nitric acid.
c. Ferrotype polish.
Benzol (benzole or benzene)________________________________15 ounces
Paraffin shavings__________________________________________75 grains
The above amount of paraffin is correct for black ferrotype tins. For chromium ferrotype tins, use 25 to 50 grains of paraffin to 15 ounces of the solvent.
d. Print bleacher (for converting prints into line drawings).
Water (cool)---------------------------------------------12 ounces
Potassium iodide_________________________________________65 grains
Iodine (black crystals)____________________________________lOgrains
Water to make--------------------------------------------16 ounces
Bleach print until image has disappeared, then fix in plain fixing bath.
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e. Gum arabic (adhesive).
Water----------------------------------------------------134 gallons
Salicylic acid---------------------------------------------160	grains
Gum arabic-------------------------------------------------  8	pounds
Glycerin--------------------------------------------------- 16	ounces
Note.—If this solution is inclined to ferment with age, the amount of salicylic acid may be increased.
/. Hypo test solution.
Water (cool, 60° F. to 70° F., preferably distilled)_______Bounces
Potassium permanganate_____________________________________4 grains
Sodium hydroxide___________________________________________8 grains
Use 14 dram (15 drops) of above solution to 8 ounces of water, preferably distilled. Pour y2 ounce of this solution in small graduate. Take equivalent of six 4- by 6-inch prints from water, drain hurriedly, and allow drippings to drip into the y2 ounce of solution for 30 seconds. The least trace of hypo in the water draining from the prints will cause this violet solution to turn to an orange color. If more hypo is present in the drippings, the solution will change to a greenish-yellow color. As certain impurities in water will cause similar discoloration of the solution, a number of drops of tap water, equivalent to number of drops to be dropped from prints, should be dropped into the y2 ounce of violet-colored solution. If no change in color takes place, any change in color that will take place from the water drained from prints will be due to the presence of hypo which will prove that the prints have not been sufficiently washed.
g. Hypo eliminator.
Water------------------------------------------------------16 ounces
Hydrogen peroxide (3 percent)--------------------------4 fluid ounces
Ammonia (3 percent)--------------------------------3% fluid ounces
Water to make----------------------------------------------32 ounces
Directions for use: Wash prints for 30 minutes at 65° F. Immerse each print for 6 minutes in hypo eliminator solution, then wash for 10 minutes and dry. Capacity of bath is about fifty 8 x 10 prints or the equivalent per gallon.
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Appendix II
LIST OF CHEMICALS
Name and chemical formula	Ounces of chemical in 100 ounces (fluid) of saturated solution at		Uses in photography
	40° F.	70° F.	
Acid, acetic	 HC2H3O2	1 M. A. P.	1 M. A. P.	Acid rinse baths, fixing baths. (Poisonous.)
Acid, citric	 h3c6h5o3	78	88	Keeper in developers, clearing baths.
Acid, hydrochloric or muriatic. HC1	M. A. P.	M. A. P.	Platinotype and carbon processes and intensification with mercury.
Acid, nitric	 hno3	M. A. P.	M. A. P.	Making emulsions, keeper in pyro developer. To clean stainless steel trays.
Acid, oxalic	 H2C2.O42H2O	7%	14%	Keeper in developers. Used in preparing potassium and ferrous oxalate. (Poisonous.)
Acid, salicylic	_ C6H4(OH) cooh	% approx.	% approx.	Preservative in glues, mucilages, and gum arabic mucilage.
Acid, sulfuric	 H2SO4	M. A. P.	M. A. P.	Fixing baths, bleachers, rinse baths, tray cleaners.
Acetone	 C3H9O	M. A. P.	M. A. P.	Solvent of celluloid, used in varnishes and film cement.
Alcohol, ethyl	 C2H5OH ”	M. A. P.	M. A. P.	Used in stock solutions of M. Q. developer to prevent crystallization. Rapid drying and cleaning.
Alum, potassium	 A12K2(SO4)324H2O	6%	11%	To harden gelatin in hardening baths and fixing baths. To purify water.
Alum, potassium chrome. K2Cr2(SO4)324H2O	15%	20%	Used in fixing baths and hardening baths for negatives.
Amidol (diaminophenol Hydrochloride). C6H3(OH)(NH4)2HC1 (1,2,4)	20%	26	A developing agent especially suited for tropical developers.
Ammonia	 NH4OH	M.A.P.	M.A.P.	To ripen emulsions, accelerator in pyro developers, as a cleaning agent.
1 Mixes all proportions.
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LIST OF CHEMICALS—Continued
Name and chemical formula	Ounces of chemical in 100 ounces (fluid) of saturated solu-		Uses in photography
	tion at 40° F.	70° F.	
Ammonium bromide	 NH4Br	52	57	Making emulsions. Restrainer in developers.
Ammonium chloride	 NH4CI	26	30	Making emulsions. Rapid fixing agent in fixing baths.
Ammonium persulfate--	52	62	Used in negative reducers.
(NH4)2S2O8			
Ammonium thiocyanate NH4CNS	62	73	Used in toning. Can be used as a silver solvent in fixing baths.
Amyl acetate	 C5HnC2H3O2	Soluble in alcohol or ether		Preparation of varnishes.
Barium sulfate	 BaSO4	Insoluble	Insoluble	Also called blanc fixA Used in making baryta paper.
Borax (sodium tetraborate) . Na2B4O7.10H2O	2%	7%	Used in toning, in developers. Acts as a restrainer with pyro and as an accelerator with hydrochinone.
Calcium chloride		Very sol-	Very sol-	Packed in containers of emul-
CaCl2	uble	uble	sions to absorb moisture.
Carbitol acetate (Diethylene glycol) (monoethyl ether acetate).	M. A. P.	M. A. P.	Used as a substitute for glycerin to soften emulsions prior to ferrotyping.
Caustic potash (See potassium hydroxide).	78	83	Accelerator in process developers. In hypo test solutions.
KOH			
Caustic soda (See sodium hydroxide).	50	83	Accelerator in process developers.
NaOH			
Diaminophenol hydro-chloride(See Amidol).	20%	26	Developing agent. Often used in tropical developers.
C6H3(OH)(NH4)2.HC1 (1, 2, 4)			
Formalin (formaldehyde) CH2O	M. A. P.	M. A. P.	40 percent formaldehyde. Used to harden gelatin in fixing baths and hardening baths. Used to prevent germicidal growths in trays, tanks, etc.
Glycerin	 C3H6(OH)3	M. A. P.	M. A. P.	Used as a solvent for some chemicals. Used to prevent curl of films and papers.
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LIST OF CHEMICALS—Continued
Name and chemical formula	Ounces of chemical in 100 ounces (fluid) of saturated solution at		Uses in photography
	40° F.	70° F.	
Glycin (Paroxyphenyl-glycin). _ _ _	Soluble ii solu 79 4% 73 Practicall	1 alkaline tion 100+ 6% 93 y insoluble	Nonstaining developing agent. Trade name: Athenon. Toning of P. O. P. and in hypo-alum-gold toning processes. Developing agent. Generally used in combination with metol. Most common fixing agent. Used in fixing baths. Farmer’s reducer and in bleaching processes. In bleachers for prints. Making blueprint paper and iron toning processes. In intensification and in solutions for combined toning and fixing. Very poisonous. Used in intensification. Very poisonous. Soluble in solution of sodium sulfite, hypo or potassium iodide. Intensification. The most used developing agent. Trade names: Elon, Rhodol, and Pictol. Developing agent, especially suitable for tropical developers. Trade name: Kodelon. Accelerator used in process developers where extreme contrast is desired.
C6H4(OH)(NH.CH2 COOH) Gold chloride			
AuC13 Hvdroquinone			
C«H4(OH)2(1, 4) Hypo (See sodium thiosulfate). Na2S2O3.5H2O Iodine			
I2 Iron (Ammono-citrate of) Fe2(NH4)2(C«H5O7)3 Lead nitrate	 Pb (NO3)2 Mercuric chloride	 HgCl2 Mercuric iodide	 Hgl2 Metol (monomethyl paramin ophenol sulfate). C6H4(OH)(NH) ch3h2so Para-aminophenol hydrochloride. C6H4(OH)(NH2).% (COOH) (1, 4) Paraformaldehyde, or trioxmethylene. (COOI2)3			
	39% 4 Insoluble 5% 1%	51 6% Insoluble 8% 2%	
			
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LIST OF CHEMICALS—Continued
Name and chemical formula Paraphenylene diamine C6H4(NH2)2 Potassium bi chromate _ K2Cr2C>7 Potassium bromide	 KBr Potassium carbonate anhydrous. K2CO3 Potassium cyanide	Ounces of 100 our of satui tion at 40° F.	chemical in ices (fluid) rated solu- 70° F. 14% 56 85 52 36 83 104 57 36% 6% 57	Uses in photography A skin irritant. Used as a fine-grain developing agent. Photo-mechanical and pigment processes, print bleachers, intensification, tray cleaners. Making emulsions. The most used restrainer. Print bleachers. Accelerator in developers. Rapid drying of negatives. Deadly poison. Used in bleachers and intensification processes. Can be used as a fixing agent for some emulsions. Used in bleachers and reducers. Accelerator in process developers. Hypo test solutions. Manufacture of emulsions, restrainer in developers, intensification, bleaching solutions. Keeper or preservative in developers. In fixing baths as an acid and preservative. Used as a developer in the platinotype process. Reducers, stain removers, tray cleaners, hypo test solutions, bleach bath in reversal process. Staining developing agent. Used only in developers for negatives.
	6% 50 83 46 30 78 99 47 29 3% 36		
KCN Potassium ferricyanide... K3Fe(CN)6 Potassium hydroxide (caustic potash) KOH Potassium iodide			
KI Potassium metabisulfite. k2s2o5 Potassium oxalate	 K2C2O4.H2O Potassium permanganate. KMnO4 Pyrogallic acid (pyro)__ ■'c6H3(OH)3(1, 2, 3)			
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LIST OF CHEMICALS—Continued
Name and chemical formula	Ounces of chemical in 100 ounces (fluid) of saturated solution at		Uses in photography
	40° F.	70° F.	
Silver bromide		Insoluble	Insoluble	Making emulsions.
AgBr			
Silver chloride		do	do	do
AgCl			
Silver nitrate	 AgNO3	109	135	Making emulsions, intensifiers, physical developers.
Sodium bisulfite	 NaHSO3	52	52	Preservative or keeper in developers. Acid and keeper in fixing baths.
Sodium bromide	 NaBr	67	73	Making emulsions. Restrainer in developer.
Sodium carbonate (anhydrous) .	10%	24	The most used accelerator in developers.
Na2CO3			
Sodium carbonate (monohydrated) .	12	28	The most used accelerator in developers.
Na2CO3.H2O			
Sodium chloride (common table salt). NaCl	31	31	Making emulsions. Restrainer in developers. Hypo-alum toning bath.
Sodium hydroxide (caustic soda).	50	83	Accelerator in process developers.
NaOH			
Sodium metaborate, crystal.	23	33	Accelerator in fine-grain and other negative developer. Trade name: Kodalk.
Sodium sulfate (anhydrous) .	5%	20%	In preparation of barium solfate. In negative develop-
Na2SO4			ers to prevent excessive swelling emulsion. Tends to coagulate gelatin.
Sodium sulfate, (crystal).	10%	41	Same uses as sodium sulfate, anhydrous.
Na2SO4.lOH2O			
Sodium sulfide (fused) _ NaS	13%	17%	Redeveloper in sepia toning. Blackener in process work.
Sodium sulfide (crystal). Na2S.9H2O	36%	47	Same uses as sodium sulfide, fused.
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LIST OF CHEMICALS—Continued
Name and chemical formula	Ounces of chemical in 100 ounces (fluid) of saturated solu-		Uses in photography
	tion at 40° F.	70° F.	
Sodium sulfite (anhydrous.) Na2SO3	17%	28	The most used preservative in developers and fixing baths. Blackener in intensification.
Sodium tetraborate (see borax). Na2B4O7.lOH2O	2%	7%	Used in toning processes. In developers acts as a restrainer with pyro and as an accelerator with hydroquinone.
Sodium thiosulfate crystal (hypo). Na2S2O3.5H2O	73	93	Most used fixing agent for silver halides. Used in fixing baths and in Farmer’s reducer.
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Appendix III
TABLES USED IN PHOTOGRAPHY
WEIGHTS AND MEASURES
Weights			
Pound (lb.)	Ounces (oz.)	Grains (gr.)	Grams (gm.)
1	16 1	7, 000 437. 5 1	453. 60 28. 35 . 065 1
		Liquid		measure		
Gallon (gal.)	Quarts (qts.)	Ounces (oz.)	Drams (dr.)		Minims (min.)	Cubic centimeters (cc.)
1	4 1	128 32 1	1, 024 256 8 1		61, 440 15, 360 480 60 1	3, 785. 44 946. 36 29. 57 3. 70 . 62
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TEMPERATURE CONVERSION
Centigrade	Fahrenheit	Centigrade	Fahrenheit
-17. 80°	0°	32. 20°	90°
-15. 00°	5°	37. 80°	100°
-12. 20°	10°	42. 20°	110°
-9. 45°	15°	48. 90°	120°
-6. 67°	20°	54. 60°	130°
-3. 89°	25°	60. 00°	140°
0° freezing point	32° of water	65. 60°	150°
4. 45°	40°	71. 10°	160°
7. 22°	45°	76. 60°	170°
10. 00°	50°	82. 00°	180°
12. 80°	55°	87. 80°	190°
15 60°	60°	93. 30°	200°
18° developing	65° temps.	98. 90°	210°
21. 10°	70°	100° boiling point of 212°	
		water	
23. 90°	75°	104. 40°	220°
26. 70°	80°	110. 00°	230°
To change Fahrenheit to centigrade: Subtract 32, multiply by 5, divide by 9.
To change Centigrade to Fahrenheit: Multiply by 9, divide by 5, add 32.
SAFELIGHTS
1 Eastman (wratten)	AGFA	Sensitized materials
Series 00	105	— All chloride papers.
0	104	All bromide papers and lantern slide plates.
0A	104	All bromide and bromo-chloride papers, lantern slides, and process film.
1	104	For ordinary, medium, and extra-fast noncolof sensitive films.
2	107	All orthochromatic emulsions.
3 6A	108	All panchromatic emulsions. X-ray films (not safe for orthochromatic materials).
	103	Ordinary panchromatic emulsions.
7		Infrared emulsion (not safe for orthochromatic or panchromatic materials).
298620°—41---21
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FILTER FACTORS
Filter	Orthochromatic		Panchromatic		Ortho-pan-chromatic		Hy per-pan -chromatic	
	Day.	Tung.	Day.	Tung.	Day.	Tung.	Day.	Tung.
Aero 1	2	1. 5	2		1. 5		1. 5	
Aero 2	2. 5	2	2. 5			2			2		
K 1	2	1. 5	2	1. 5	1. 5	1 5	1. 5	1. 5
K 2	2. 5	2	2. 5	2	2	1 5	2	1. 5
K 3	2. 5	2	2. 5	2	2	1. 5	2	1. 5
NO 12	3	2. 5	3	2. 5	2	1. 5	2	1. 5
G	5	3	4. 5	3	3	2	2. 5	2
F					12	5	15	8	8	4
A					8	4	7	4	4	2
B	8	4. 5	12	9	6	6	7	6
C 4	9	12	10	15	12	24	12	24
C 5	3	3. 5	3	5	5	10	5	10
X 1	—	—	—	—	—	3	5		
X 2	—	—	—	—	—	—	—	5
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FILM SPEED RATINGS
Weston	General Electric	H and D	Scheiner
0. 2	0. 3	9	2
. 5	. 8	23	6
1	1. 5	45	9
2	3	91	12
3	5	150	14
4	6	190	15
5	8	240	16
6	10	308	17
8	12	390	18
12	20	636	20
16	24	800	21
24	40	1, 300	23
32	50	1, 700	24
40	64	2, 100	25
50	80	2, 700	26
64	100	3, 500	27
100	160	5, 600	29
128	200	7, 200	30
160	250	9, 000	31
200	300	11, 500	32
240	360	12, 800	33
300	450	16, 800	34
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Density	Transmission (Percent)
0. 10	79. 4000
. 15	70. 8000
. 20	63. 1000
. 302	50. 0000
. 450	35. 5000
. 600	25. 0000
. 750	17. 8000
. 900	12. 6000
1. 000	10. 0000
1. 300	5. 0000
1. 600	2. 5000
1. 900	1. 2600
2. 000	1. 0000
2. 300	. 5000
2. 600	. 2500
2. 900	. 1256
3. 000	. 1000
1
Density = Log. O = Log.~
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Appendix IV
GLOSSARY OF TERMS
Aberrations. Errors in the performance of a lens which cause defects in photographs by distortion of light rays passing through the lens.
Abrasions.—Streaks occurring on emulsion surfaces which appear like pencil marks or scratches.
Accelerator.—Any substance which increases the activity of a developing agent and shortens developing time or the time in which an image appears.
Achromatic lens.—A lens which is partially corrected for chromatic aberration and brings red and green light rays to approximately the same plane of focus. Achromatic correction is obtained by cementing a positive lens of crown glass with a negative lens of flint glass.
Actinic.—Light which is capable of causing photo-chemical change in a sensitive emulsion. Actinic value varies with the sensitivity of the material. Blue and violet are the most actinic of the visible light rays.
Additive process.—Pertains to color photography. A process by which various visible colors are obtained by mixing or adding primary colors. Yellow for example is a mixture of red and green light rays in the proper proportion.
Affinity. The readiness with which substances react with one another. Generally pertains to chemical reaction, and in photography, sodium sulfite has an affinity for oxygen thereby preventing oxidation of the developing agent in a developer.
Agitation.—The process of stirring or circulating a photographic solution to bring fresh solution in contact with the material which is being treated. This may be done by moving the material in the solution as in tank development, or by moving the solution itself as in tray development.
Air bells.—Small bubbles or spherical masses of air which attach to the surface of an emulsion and leave a small area unaffected by the solution. Can be removed by vigorous agitation of the solution.
Anastigmat.—A. lens which has been corrected for astigmatism and thereby focuses vertical and horizontal lines with equal brightness and definition. Anastigmatic lenses are also free from other common aberrations.
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Anhydrous.—Refers to chemical salts which contain no water of crystallization. Identical in meaning with “desiccated” which refers to dry chemicals.
Antihalation backing.—A coating, usually gelatin, on the back of a film containing a dye or colored pigment for the purpose of absorbing light rays, thus preventing their reflection from the back surface of the film base.
Aperture.—A small opening, usually circular, in a plate or sheet. In cameras, the aperture is usually variable in the form of an iris diaphragm and regulates the amount of light which passes through the lens.
Apochromatic.—Refers to lenses which are completely corrected for chromatic aberration. Focuses rays of all colors to very nearly the same plane.
Back focus.—The distance from the back or rear surface of a lens to the focal plane when the lens is focused at infinity. It is used in determining the length of camera bellows suitable for a given lens.
Blisters.—Small bubbles formed under an emulsion due to the detachment of the emulsion from its base.
Blow-up.—Photographic slang for enlarging.
Brightness range.—Variation in intensity from maximum to minimum. Generally refers to a subject to be photographed. For example, a particular subject may have a range of one to four, that is, the brightest highlight of the subject has four times the amount of light reflected from it as the least bright portion of the subject.
Brilliance.—A term denoting the degree of intensity of a color.
Cable release.—A flexible shaft for operating a camera shutter at a distance. Used to avoid camera movement when operating the shutter release lever with the hand.
Camera.—A device used for taking photographs consisting of a lightproof chamber, a lens, a means for focusing, a shutter and diaphragm to regulate exposure, and a means for holding a sensitized film or plate.
Cellulose acetate.—Main constituent of safety base film. Burns very slowly and is preferable to nitrate base.
Cellulose nitrate.—Base material for nitrate film base. Highly inflammable.
Chemical fog.—Fog produced in a sensitive emulsion by any chemical means. Often caused by very energetic or contaminated developer.
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Cinematography.—The process of making motion pictures.
Circle of confusion.—The size of the image of a point formed by a lens. Should not be larger than (doo"inch in diameter. If a negative is to be enlarged, this circle should be considerably smaller than Vioo inch. This diameter is the maximum to produce a sharp image with the lens.
Color.—The property of an object which depends on the wave length of light it reflects. The sensation produced in the eye by a particular wave length or group of wave lengths of visible light.
Color sensitivity.—The sensitivity of a photographic emulsion to light of various wave lengths.
Composition.—A term referring to the grouping of objects in a photograph to obtain proper balance and accentuation of the main subject.
Condenser.—A lens used to collect rays of light from a source and project them in proper alinement to obtain even and undistorted illumination of a negative or positive. Used in condenser type enlarger and projection lanterns.
Contact print.—A print made by placing a sensitized emulsion in direct contact with a negative and passing light through the negative.
Contrast.—The difference between light intensities in a subject area such as between highlights and shadows. In a negative, the difference is between density values and in a print it is the reflective power between highlight and shadow.
C onvertible lens.—A lens containing two or more elements which can be used individually or in combination.
Covering power.—The capacity of a lens to give a sharply-defined image to the edges of sensitized material it is designed to cover and at the largest possible aperture.
Darkroom,.—A room for photographic operations, mainly processing, which can be made free from white light and is usually equipped with safelights emitting nonactinic light.
Definition.—The degree of sharpness of a photographic image dependent upon perfection or accuracy of the lens used to obtain the image.
Deliquescent.—The property of a chemical salt of absorbing moisture directly from the atmosphere.
Densitometer.—A device for measuring the density of a silver deposit in a photographic image. It is usually limited to measuring even density in very small areas. Density is the expression for
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denoting amount of light absorbed by a medium in relation to the light incident on it.
Desensitizer.—An agent for decreasing the color sensitivity of a photographic emulsion to facilitate development under comparatively bright light. The action is applied after exposure.
Developer.—A solution used to make visible the latent image in an exposed emulsion.
Diffusion.—The scattering of light rays upon reflection from a rough surface, or the transmission of light through a translucent medium.
Dispersion.—The separation of individual colors of light by differential refraction.
Distortion.—Defects in a photographic image by abnormal rendition perspective.
Dodging.—The process of holding back light from certain areas of the sensitized paper in making a print to avoid overprinting those areas. In projection printing, it is accomplished by inserting an opaque medium of proper shape and size between the lens and the easel and in contact printing, by either varying the illumination in given areas of the negative or inserting translucent or opaque paper between the light source and the negative.
Dry mounting.—A method for cementing a print to a mount by means of a thin tissue of thermoplastic material. The tissue is placed between the print and the mount and sufficient heat applied to melt the tissue. The tissue is usually impregnated with shellac which melts in the presence of sufficient heat.
Dyes, sensitizing.—Dyes used to extend the color sensitivity of silver halide. Applied in the manufacture of emulsions to obtain selective sensitivity to colored light.
Easel.—A device to hold sensitized paper in place before an enlarger. Generally includes an adjustable mask to accommodate different sizes of paper.
Effective aperture.—The maximum diameter of a lens as used for projection of images. This diameter is used in computing ff numbers.
Efflorescence.—The process by which a chemical salt loses its water of crystallization upon exposure to air.
Embossing.—The process by which the central portion of a print or mount is depressed, leaving a raised margin.
Emulsion.—The sensitive coating on films, plates, and papers composed of silver halide crystals suspended in gelatin.
Enlargement {projection print).—A photographic print made by projecting a negative to obtain an enlarged image on sensitized paper.
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Exhaustion.—The state reached when the principal ingredient of any photographic solution is no longer active.
Exposure.—The length of time during which a given intensity of light is allowed to act upon a sensitive emulsion. Technically, it is the product of the time and the light intensity.
Exposure meter.—An instrument for measuring light intensity and determining correct exposure. It is calibrated for different emulsion speeds.
Fast lens.—A lens of relatively large aperture //4.5, //3.5, and //2 are considered fast apertures for lenses.
Feather edge.—The edge of a print which has been treated with sandpaper or emery paper, and tapers from a very thin edge to the full thickness of the print. Its application is in assembling aerial mosaic prints to obtain a smooth joint between prints.
Ferrotype plates.—Sheets of thin enameled or chromium-plated iron used in obtaining high gloss of print. Some plates are made of polished stainless steel.
Fixing.—The process of removing the unexposed and undeveloped silver halide from a negative or print.
Flat.—Expression denoting lack of contrast in a print or negative. Flatness of field.—The quality of a lens which affords sharpness of image both in the center and at the edges of the negative.
Focus.—The point toward which the rays of light converge to form an image after passing through a lens.
Focusing scale.—A graduated scale for different distances which permits focusing without the aid of a focusing screen.
Focusing screen.—A sheet of ground glass on which the image is focused and composed before exposure.
Forcing.—Attempting to bring out detail in an underexposed film, plate, or print by prolonged development or by the addition of an accelerator. Likely to produce fog.
Frilling.—The puckering up and detachment of the emulsion from the support around the edges; happens most often in hot weather or because of too much alkali in the developer.
Gamma.—A numerical measure of contrast in the development of a negative.
Gradation.—The range of tones from the brightest highlights to the deepest shadows.
Graininess.—The effect produced when the silver grains of a developed negative or print become visible. The relative sizes of grains determine the degree of graininess.
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Halation.—A blurred effect, resembling a halo, usually occurring around bright objects; caused by reflection of rays of light from the back of negative material.
Halftones.—All gradations between highlights and shadows.
Halogen.—Iodine, bromine, chlorine, and fluorine are known as the halogens. Salts of these elements are called “halides.”
Hard.—Used to denote excessive contrast.
Highlights.—Those portions of a subject upon which the greatest amounts of light fall. The densest parts of a negative and the lightest parts of prints.
Hydrometer.—An instrument used in photographic chemical mixing to find the concentration of a single chemical in water. Most common use is in mixing large quantities of hypo.
Hyper-panchromatic.—Term used to designate films and plates which have a high red sensitivity.
Hypo.—Abbreviation for the compound sodium thiosulphate, the most common fixing agent.
Imbibition.—Used in color photography. Process of dye transfer in the wash-off relief process.
Infinity.—Any great distance from a camera lens beyond which light rays from any point to the lens are regarded as parallel.
Infrared.—Invisible rays of light below the visible red. They extend from 700 to 13,000 millimicrons in wavelength.
Intensification.—The process of building up the density of a photographic image by chemical means.
Intensity (light).—The quantity of light emitted or reflected from a given source.
Irradiation.—The spreading of an image due to internal reflections within an emulsion. Causes a lowering of definition of the image.
Keeper.—An acid chemical added to developers to keep them in usable condition without oxidation of the developing agent with lapse of time.
Laboratory.—a. The plant or accomodation which permits photographic personnel and equipment to function.
b. The equipment and personnel allotted a photographic plant or accommodation.
Latent image.—The invisible image recorded by light action upon the film or plate and which is made visible in development.
Latitude.—a. Exposure.—The quality of a film or plate which allows variation in exposure without detriment to image quality.
b. Development.—Allowable variation in the recommended developing time without noticeable difference in contrast.
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Light fog.—A graying of the image, produced by an unsafe darkroom lamp or accidental exposure to white light.
Matrix.—A positive print used in the wash-off relief process to hold the dye used in making the final print by imbibition.
Meter-candle-second.—Unit of exposure in sensitometry. The product of illumination or intensity in meter-candles and the exposure time in seconds.
Milky.—Appearance of an incorrect fixing bath; often the result of impure chemicals or improper mixing.
Mottled.—Irregular spots on negatives or prints.
Negative.—A photographic image on film, plate, or paper in which the dark portions of the subject appear light and the light portions appear dark.
Opaque.—Refers to an object which is incapable of transmitting visible light.
Ortlwchromatic.—Refers to films or plates whose sensitivity is to violet, blue, yellow, and green and which are insensitive to red.
Orthochromatic rendition.—In ordinary photography, this refers to the reproduction of color brightnesses in their relative shades of gray. In color photography, it is the reproduction of color as color.
Orthonon.—Name given to color-blind or noncolor sensitive emulsions.
Ortho-panchromatic.—Panchromatic emulsions which most nearly approximate the sensitivity of the eye.
Panchromatic.—Emulsions which are sensitive to all visible colors. Photomontage.—A composite picture made by a number of exposures on the same film, by projection of a number of negatives to make a composite, or by cutting and pasting up a number of prints and subsequently copying to a new negative, or any similar method of making a composite print.
Photosensitive.—A term used to describe substances whose chemical composition is altered by the action of light.
Photostat.—A camera used to produce copies of documents, drawings, or photographs. The term also applies to the copy made with this type of camera.
Pinholes.—Minute transparent spots in negatives which show up as black spots in prints, most frequently caused by dust on the film.
Plane-parallel.—A term used to describe filter glasses whose faces are ground to flat, parallel surfaces.
Portrait.—A photograph of an individual; usually refers only to a head or head and shoulders.
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Production.—The section or sections of a photographic laboratory which engage in or assist photographic processes. The product or products of photographic laboratory operation.
Proportional reducer.—A reducing solution 'which reduces the shadows at the same rate as the highlights and therefore produces no change in contrast.
Radiant energy.—A form of energy of electromagnetic character. All light which causes photo-chemical reduction is radiant energy.
Reducing agent.—Refers to development. The active ingredient of a developer which changes the subhalide to metallic silver. Usually requires acceleration.
Reflection.—The diversion of light from any surface.
Refraction.—The bending of light rays when passing from one medium to a medium of different density.
Refractive index.—The ratio of the speed of light in one medium to the speed in a medium of different density, or the ratio of the density of a medium to the density of air. Air is usually considered the standard medium in computing refractive index.
Relative speed of emulsions.—The rate at which one emulsion will record an image as compared with a standard emulsion of known sensitivity. Relative speeds are used in most speed rating systems.
Resolving power.—The measure of the ability of an emulsion to record fine detail. Fine-grain emulsions have high resolving power.
Restitution.—Projection printing for the purpose of minimizing variation in scale of prints from the true average scale.
Restrainer.—The chemical in a developing solution which holds back or checks the action of the developing agent.
Retouching.—The removal or softening of defects in a negative by means of pencil lines or color.
Scale.—Scale is the ratio of distance in the subject to the corresponding distance in the photograph.
Screen process.—A process incorporating minute colored particles, with the film or plate separate from the emulsion. The negative is exposed and reversed chemically to yield a positive. The grains which correspond in color to the original show through the emulsion and the remaining grains which do not correspond to the original are obscured by the overlying silver image.
Secondary color.—A color formed from the combination of two primary colors. Yellow, magenta, and cyan (blue-green) are the secondary colors.
Sensitometry.—The measurement of the response of a photo-sensitive material to the action of light.
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Speed of an emulsion.—The rate at which an emulsion will record an image after it has been acted upon by light.
Speed rating.—An arbitrary number assigned to a photographic emulsion to designate its sensitivity in comparison with other emulsions. The individual numbers within a separate rating system are comparable with each other but not with the numbers of another system.
Spotting.—Retouching on prints with spotting colors or pencils.
Squeegee.—A strip of soft rubber mounted in a wooden frame or roller used for squeezing moisture from prints.
Stock solution.—Photographic solution in concentrated form which is diluted for use.
Subhalide.—Halides, generally referring to silver, which have been reduced from the halide form by the action of light.
Subtractive process.—Refers to color photography, a process in which two or more negatives are made through filters which subtract all but the desired color for each negative, and also in color printing processes in which the color desired is obtained by subtraction in a pigment or silver toning process.
Subtractive reducer.—A reducer which affects the shadows in a negative without noticeably affecting the highlights and thereby increases the contrast in the negative.
Superproportional reducer.—A reducing solution which lowers highlight density faster than it affects shadow density. The result is a lowering of the contrast of a negative.
Synchro-flash.—A term applied to photography in which a flash bulb is ignited at the same instant that the shutter is opened.
Synchronizer.—A device for operating a shutter simultaneously with the firing of a flash bulb.
Time gamma curve.—A curve of developing time plotted against develop-contrast or gamma. The contrast for any given time may be read directly from the curve, or vice versa. The curve applies for only one developer and one particular emulsion.
Tone.—Each distinguishable color or shade from black to white.
Toning.—The chemical treatment of a photographic image to obtain a colored image from a black and white one.
Translucent.—Semitransparent. A substance which passes light but diffuses it so that objects cannot be clearly distinguished.
Transparency.—A positive image on a clear base which must be viewed by transmitted light. Also refers to the light transmitting power of the silver deposit in a negative and is the inverse of opacity.
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Vignette.—Ordinarily refers to projection printing. A process of regulating the distribution of light which reaches the print in such a way that the image obtained fades out toward the edges.
Weak image.—The image on a print or negative which is lacking in contrast and density.
Working aperture.—The largest diaphragm opening at which a lens will give satisfactory definition over the area of a film or plate which is covered by an image.
Working solution.—A photographic solution which has been diluted from a stock solution and is ready for use.
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INDEX
Paragraph
Aberration_________________________________________________ 135
Absorption_________________________________________________ 120
Accelerator________________________________________________ 31, 32
Acid:
Acetic------------------------------------------------ 46-55
Boric____________________________________________________ 47
Fixing bath______________________________________________ 45
Hardener______________________________________________ 46, 47
Pyrogallic-------------------------------------------- 26-30
Rinse____________________________________________________ 55
Adhesives:
Classification__________________________________________ 304
Dry mounting tissue_____________________________________ 309
Glue and mucilage_______________________________________ 309
Gum arabic______________________________________________ 309
Photo paste_____________________________________________ 309
Rubber cement___________________________________________ 309
Aerial films_______________________________________________ . 105
Aerial photography___________________________________________ 382
Alcohol______________________________________________________ 259
Alkalis----------------------------------------------------31, 32
Alteration of equipment______________________________________ 406
Amidol________________________________________________________ 30
Anastigmat lens______________________________________________ 135
Angle of field_______________________________________________ 131
Angle of view________________________________________________ 132
Antihalation__________________________________________________ 98
Aperture_____________________________________________________ 351
Apochromatic_________________________________________________ 135
Application of sensitometry________________________________ 172, 173
Artificial illumination____________________________________ 355, 381
Baryta______________________________________________________ 113
Borax__-____________________________________________________  32
Boric acid______________________________________________'	47
Bromide emulsion____________________________________   26,27,111
Bromo-chloride emulsion_____________________________________ 111
Calculation of exposure_____________________________________ 219
Cameras:
Copying---------------------------------------- 176,	350-353
Hand------------------------------------------- 176,	181-187
View------------------------------------------- 176,	177-180
Carbro process_____________________________________2________ 379
Care of equipment________________________________________ 415
Page
87
76 21,22
30
30
29
30 14
34
232
235
235
235
235
235 66
274
187
21, 22 293
19
87
85
86
61
254
87 117, 118 256, 273
72
22
30
14, 15, 71
71
154
120, 254
120, 124
120, 121
271
299
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INDEX
Paragraph
Care of filters______________________________________________ 143
Care of lens_________________________________________________ 137
Characteristics of light------------------------------------- 120
Chemical mixing_____________________________________________86-91
Chemicals, care_____________________________________________   74
Chemicals, characteristics______________________________ 71—73, 75, 76
Chemicals, list_________________________________________ App. II
Chemical solutions______________________________________ 22, 77-81
Chloride emulsion_____________________________________________ 26
Choice of negative emulsions_________________________________ 105
Chrome alum___________________________________________________ 48
Chromatone process___________________________________________ 379
Circle of confusion_________________________________________  126
Cleaning a lens______________________________________________ 136
Code designation--------------------------------------------  273
Collodion_____________________________________________________ 25
Color___________________________________________________ 146, 376
Color blind emulsion______ __________________________________ 103
Color elimination____________________________________________ 149
Color exaggeration___________________________________________ 149
Color photography:
Applications_________________________________________ 386-388
Definition_______________________________________________ 376
Emulsions in_____________________________________________ 117
Types-'. ________________________________________________ 377
Color printing_______________________________________________ 379
Color reproduction______________________________________ 378, 379
Color sensitivity:
Color-blind emulsions____________________________________ 103
Infrared emulsion________________________________________ 103
Orthochromatic___________________________________________ 103
Panchromatic_____________________________________________ 103
Range_____________________________________________________ 99
X-ray emulsions__________________________________________ 116
Color transparency___________________________________________ 373
Commercial emulsions_________________________________________ 105
Complementary colors_______________________________________   145
Composition:
Definition______________________________________________  188
Exterior subjects____________________________________ 191,192
Interior subjects____________________________________ 193-196
Rules____________________________________________________ 190
Composition of a filter_____________________;______________	139
Compounds__________________________________________________ 23, 24
Conjugate distances_____________________________________ 133, 348
Contrast:
Definition__________________________________________ 101, 239
Determination____________________________________________ 163
Inherent_________________________________________________ 104
Negative emulsions_______________________________________ 104
Papers___________________________________________________ 112
Page
92
88
76
56
51
50, 51
314
12, 51
14
66
30
271
83
88
205
14
95, 268
66
98
98
277
268
73
268
271
268, 271
66
66
66
66
62
73
267
66
93
127 129, 132 133, 134
128
89
13
86, 252
63, 169
108
66
66
71
336
INDEX
Construction of a filter___. _
Conversion, table for temperature Cooling, water and solutions____
Copying:
Definition__________________
Development in______________
Lens used in________________
Mosaic______________________
To scale____________________
Covering power of a lens________
Cut films_______________________
Daylight illumination:
Color photography___________
Copying_____________________
Defects on prints_______________
Definition of lens______________
Densitometer____________________
Density:
Definition__________________
Exposure relation___________
Measurement of
Depth of field_____________
Depth of focus_____________
Developer ingredients______
Developing agents__________
Development:
Contrast________________
Color photography_______
Film slides_____________
Lantern slides__________
Latitude________
Mosaic copy negatives. _
Sensitometric strips____
Temperature_____________
Diffusion___________________
Dispersion__________________
Drying:
Negatives_______________
Prints__________________
Duplication of negatives'.__
Emulsion coatings___________
Emulsion, lantern slide
Emulsion properties_________
Emulsion speed:
Definition______________
II and D________________
Methods of expressing___
Minimum useful gradient
Threshold___________
Weston__________________
298620° 41------22
337
Paragraph
Page
App.
316-;
... 160, 160, 162,
139 III 254	89 321 184
341	251
347	252
353	255
343	251
348	252
131	85
106	68
382	274
228	160
340	242
130	85
161	106
241	104, 170
233	104,
	106, 165
161	106
128	84
129	85
29	18
30	19
383-
301,
265,
159	104
5-385	274
370	266
365	264
166	111
347	252
159	104
364	263
120	76
120	76
247	180
, 302	227, 228
, 266	189, 190
96	60
362	263
94	59
100	63
169	113
168	113
169	113
169	113
169	113
INDEX
Paragraph Page
Emulsion support______________________________________________ 95	59
Emulsions for reproduction___________________________________ 354	255
Engineering photographs-------------------------------------- 198	136
Exhausted developer___________________________________________ 36	25
Exhausted fixing bath, tests for______________________________ 54	33
Exposure:
Color photography____________________________________ 383, 384	274, 276
Determinations_______________________________________ 224	155
Factors______________________________________________ 220,356	154,258
Latitude_____________________________________________ 170	116
Meters_______________________________________________ 222, 223	155
Modification______________________—_----------------- 150	98
Tables and guides----------------- —	----------- 225	156
Exposure and density------------------ ------------------ 223, 224	155
Ferrotyping__________________________________________________ 302	228
Film packs___________________________________________________ 106	68
Films and negatives------------------------------------------ 406	293
Filter:
Action___________________________________________________ 141	90
Definition_______________________________________________ 138	89
Factors__________________________________________________ 142	92
Purpose-------------------------------------------------  140	90
Fine grain development----------------------------------  248-252	182
Finishing of prints-------------------------------------- 298-304	223
Fire exits, signs, etc--------------------------------------- 418	300
Fire extinguishers___________________________________________ 419	300
Fixing baths:
Acid_____________________________________________________  45	29
Acetic acid hardening------------------------------------- 46	30
Boric acid________________________________________________ 47	30
Capacity of----------------------------------------------  53	32
Chemicals used------------------------------------------   39	27
Chrome alum----------------------------------------------  48	30
Double_________________________________________________    52	32
Functions________________________________________________  38	27
Plain_____________________________________________________ 44	29
Rapid____________________________________________________  50	31
Test for strength---------------------------------------   54	33
Time of fixation in--------------------------------------  51	31
Tropical__________________________________________________ 49	31
Flashlight photography___________________________________ 212-218	150
Focal length------------------------------------------------  123	79
Focal plane__________________________________________________ 122	78
Focus________________________________________________________ 122	78
Formulary________________________________________________ App. I	303
Gamma:
Definition_______________________________________________ 163	108
Determination____________________________________________ 164	109
Infinity_________________________________________________ 167	111
338
INDEX
Paragraph
Gammeter__________________________________________ _	^4
Gelatin___________________________________________ _	25
Glossary of terms_______________________________________ App jy
Graininess______________________________________________ 1Q2 248
Ground photography___________________________________________ 388
Hand cameras_____________________________________________ 181-187
Halation__________________________________________ __ __	98
H and D curves_______________________________________________ 162
H and D speed measurement___________________________________  169
Hardening baths_________________________________________ App. I, 56
Haze________________________________________________________    148
High speed photography_______________________________________ 211
Hydroquinone______1_____________________________________ _	39
Hyperfocal distance__________________________________________ x27
Hypo test solution____________________________________________ 61
Identification photographs______________________________ 200 201
Illumination in color photography________________________ 380-382
Infrared photography_________________________________________ 151
Inherent contrast_____________________________________________112
Intensification of negatives:
Chromium intensifier____________________________________   65
Mercuric intensifier______________________________________ 65
Mercuric iodide intensifier_____________________________   65
Procedure_________________________________________________ 65
Purpose___________________________________________________ 62
Interior group photography___________________________________ 199
Inverse square law_________________________________________   125
Irradiation___________________________________________________ 94
Keepers_______________________________________________________ 34
Laboratory:
Electricity in___________________________________________ 416
Flexibility_____________________________________________  395
Light and power in_______________________________________ 395
Location_________________________________________________ 407
Moving--------------------------------------------------- 395
Types-----------------------------------------------394, 395
Ventilation______________________________________________ 499
Water in--------------------------------------------- 395,416
Lantern slide emulsions______________________________________ 109
Lantern slides:
Binding-------------------------------------------------- 366
Definition_______________________________________________ 358
Marking-------------------------------------------------- 366
Masking-------------------------------------------------- 366
Lens----------------------------------------------------_	121
Light, characteristics__________________________________ 119, 120
List of chemicals_______________________________________App. II
Loan of equipment____________________________________________ 397
Page
109
14
325
63, 182
278
124
61
106
113
303, 35
95
150
19
84
38
141
273
99
71
44
44
44
44
40
140
81
59
24
299
280
280
295
280
280
296
280, 299
70
265
262
265
265
78
75, 76
314
282
339
INDEX
Paragraph Page
Micro-copies________________________________________________ 367	266
Monomethyl-para-aminophenol sulfate__________________________ 30	19
Motion picture positive film________________________________ 109	70
Mounting photographs_____________________________________306-315	234
Moving objects, photography of__________________________ 206-211	145
Negative, blocking out______________________________________ 272	202
Negative defects________________________________________ 268-269	191
Negative developing:
Factors in development______________________________ 235, 236	168
Fine grain__________________________________________ 248-250	182
Handling of film________________________________________ 245	175
Methods_____________________________________________ 243-246	174
Speed processing____________________________________ 255-264	186
Tank____________________________________________________ 246	178
Time and temperature method----------------------------- 242	173
Tray____________________________________________________ 245	175
Tropical____________________________________________ 253, 254	184
Negative making:
Importance______,--------------------------------------- 226	159
Perfect negatives_______________________________________ 232	165
Negative spotting_______________________________________ 270,271	201,202
Nine representatives of negative making--------------------- 241	170
Opaque______________________________________________________ 120	76
Optics______________________________________________________ 118	75
Organization of a photographic unit:
System of work______________________________________ 402, 403	285
Allocation of personnel--------------------------------- 404	286
Chemical mixing section_________________________________ 408	296
Camera repair section___________________________________ 410	297
Functions within the unit___________________________ 389-393	279
Service test equipment__________________________________ 414	299
Experiments_____________________________________________ 413	298
Orthochromatic rendition____________________________________ 148	95
Paraformaldehyde--------------------------------------------- 32	22
Photographic files and reports______________________________ 405	286
Photographic work, authority for____________________________ 399	283
Polarizing filters__________________________________________ 150	98
Potassium bromide--------------------------------------- 26, 33	14, 23
Potassium carbonate------------------------------------------ 32	22
Potassium iodide---------------------------------------- 26, 33	14, 23
Preservers______________________________________________35, 39, 43 25, 27, 28
Preservatives------------------------------------------- 32, 35	22, 25
Prirpary colors_____________________________________________ 144	93
Print defects___________________________________________ 316-340	242
Printing, definition---------------------------------------- 275	206
Printing, aerial mosaic:
Green tones_____________________________________________ 291	213
Precautions and directions------------------------------ 289	213
Procedure_______________________________________________ 288	211
Requirements____________________________________________ 288	211
340
INDEX
Printing, aerial mosiac—Continued.	Paragraph Page
Soft prints from contrasty negatives_____________________ 290	213
Use of potassium	bromide______________________________ 291	213
Use of potassium	sulfocyanate____________________________ 292	214
Printing, contact:
Development______________________________________________ 284	209
Dodging-------------------------------------------------- 282	209
Fixation------------------------------------------------- 286	210
Procedure________________________________________________ 279	208
Rinsing-------------------------------------------------- 285	210
Safelights----------------------------------------------- 283	209
Washing__________________________________________________ 287	211
Printing, projection:
Developing_______________________________________________ 297	217
Dodging-------------------------------------------------- 297	217
Fixing--------------------------------------------------- 297	217
Method--------------------------------------------------- 293	215
Operations involved______________________________________ 297	217
Projection printers_________________________________ 294, 296	215, 217
Types of paper------------------------------------------- 295	216
Washing__________________________________________________ 297	217
Print straightening___________________________________________ 303	232
Print trimming________________________________________________ 304	232
Procurement, records_____________________________________ 391, 393	280
Pyrogallic acid________________________________________________ 26	14
Range finders_________________________________________________ 187	126
Reduction:
Definition________________________________________________ 62	40
Proportional reducer______________________________________ 64	41
Subtractive reducer_______________________________________ 64	41
Superproportional reducer_________________________________ 64	41
Reflection____________________________________________________ 120	76
Refraction____________________________________________________ 120	76
Representative negatives______________________________________ 241	170
Reproduction of color_________________________________________ 147	95
Resolving power of emulsions__________________________________ 102	63
Resolving power of lenses________________________________ 134, 356	86, 258
Restrainer_____________________________________________________ 33	23
Safelights:
For bromide paper________________________________________ 295	216
For chloride paper_______________________________________ 283	209
For negative materials___________________________________ 117	73
Sensitometer__________________________________________________ 156	102
Sensitometry:
Application_________________________________________ 172, 173	117, 118
Definition_______________________________________________ 152	101
Exposure in______________________________________________ 156	102
Scope____________________________________________________ 153	101
Setting up a view camera______________________________________ 177	121
Silver bromide__________________________________________________ 26	14
341
INDEX
Paragraph
Silver grains__________________________________________________ 28
Silver halide_______________________________________________ 26 41
Silver nitrate_________________________________________________ 26
Silver solvent_________________________________________________ 39
Size and scale of photographs_________________________________ 348
Sodium carbonate_______________________________________________ 32
Sodium chloride_____________________________________________ 26, 33
Sodium hydroxide____________________________________________■_	32
Sodium metabisulfite________________________________________ 34
Sodium metaborate___________________________________________ 32
Sodium sulfite______________________________________________ 32 35
Sodium thiosulfate__________________________________________ 39 41
Specular light________________________________________________ 150
Speed, emulsion______________________________,________ 100, 104 111
Speed of a lens_______________________________________________ 125
Speed processing__________________________________________ 255-264
Tables used in photography_______________________________ App. III
Tones---------------------------------------------------- 229, 230
Toning:
Definition________________________________________________ 66
Sepia---------------------------------------------------67-69
Training of personnel_________________________________________ 400
Transmission__________________________________________________ 120
Transparencies---------------------------------------- 109, 358-374
Trimming prints_______________________________________________ 304
Ultraviolet_________________________________________________ 151
Underdevelopment______________________________________________ 241
Underexposure_________________________________________________ 241
Vertical tilt_________________________________________________ 180
View camera_______________________________________________ 176-180
Washing------------------------------------------------------57-60
Water__________________________________________________________ 84
Working aperture______________________________________________ 356
X-ray emulsions_______________________________________________ 116
[A. G. 062.11 (1-3-41).]
Page
16
14, 27
14
27
252
22
14, 23
22
24
22
22, 25
27
98
63, 66, 71
81
186
320
160, 161
47
47
283
76
70, 262 232
99 170 170
121
120
35
54
258
73
By order of the Secretary of War :
Official, :
E. S. ADAMS,
Major General, The Adjutant General.
Distribution ;
G. C. MARSHALL,
Chief of Staff.
B (2) ; R and H 1 (6) ; R 2, 4, 6, 7, 10, 17 (2), 5 (5) ; Bn 1, 5, 11 (2); IBn 1 (10) ; C 11 (2).
(For explanation of symbols, see FM 21-6.)
342
0. S. GOVERNMENT PRINTING OFFICE: 1941
For sale by the Superintendent of Documents, Washington, D. C.
Price 35 cents
NTSU LIBRARY

UNT LIBRARIES DENTON TX 76203
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