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The purpose of any negative material is to record the image focused upon it by the camera lens. The negative reproduces the lights and shadows of the subject in reverse but with the same tone value. The light areas of the subject are shown as dense silver deposits. Lighter or thinner deposits of silver represent the shadow or darker areas of the subject.

Many substances are affected in some way by light. The substances of the photographic principle are the salts of silver. The elements used in photography are chlorine, bromine, and iodine.

When one or more of these elements combine with silver, a compound is formed that is light sensitive. Other metals such as gold and platinum are also light sensitive when combined with silver, but they are too expensive to use.

Light sensitive materials are made of two basic parts; the emulsion and the base. The emulsion is the light sensitive surface while the base is the support for the emulsion.

Physical Properties--Film consists of: a film base, antihalation properties, emulsion, Noncurl Coating, and a protective over coating.

• Film Bases--The most common base is a polyester base called an estar base. This used to be cellulose, however scientists have found that the "estar" base offers more dimensional stability.

• Annihilation Properties--When light is reflected back through the emulsion and through the base, it is known as halation and as a result the image is not as sharp. There is a double image or like a halo around the image. A dye is used to prevent this. Usually the dye is purple; however new advances have been made to prevent an effect known as light piping. Light piping is when light strikes the edge of roll film. It will fog the film by traveling to and from in a zig zag fashion. To stop light piping a gray dye is used which is dissolved during development.

• Emulsion--The emulsion is a thick layer of gelatin in which is a suspended microscopic crystal of light sensitive silver salts.

• Noncurl Coating--A coat of hardened gelatin on the backside of film to prevent curling when the expanded wet emulsion dries.

• Protective over Coating--A clear gelatin base material is used to protect the emulsion from abrasion.

Any time film is moved and there is friction the film will obtain a charge and will try to discharge as soon as possible causing a branch like effect on the negative. These are called static markings.

To prevent static, do the following: avoid sudden movements when handling film; do not wind or unwind rolls rapidly; when removing the interleaved paper, do not pass the film between your fingers.

An emulsion is a think layer of gelatin in which is suspended microscopic crystals of light sensitive salts.

The emulsion is made in the following manner:

1. The gelatin is soaked in water until it is swollen and then is dissolved by heating.
2. A solution of bromide and iodide, with or without ammonia, is added and thoroughly mixed into the gelatin solution.
3. A quantity of silver nitrate is then dissolved in water and added; the rate, temperature, and all other factors are carefully controlled. The nitrate is added in complete darkness and when this step is completed the solution is called an emulsion.
4. This step is called ripening. The emulsion is heated from 120 degrees to 175 degrees to recrystallize the silver bromoiodide and to fix the size and frequency of the silver halide grains.
5. More gelatin is added and mixed with the emulsion and then chilled.
6. The chilled emulsion is allowed to set to a jelly-like form and is then shredded into small noodles.
7. The shredded emulsion is washed to remove the excess salts.
8. The washed emulsion is reheated to help the forming of sensitizing specks on the silver halide grains. This step is called after ripening. This process increases the sensitivity of the emulsion.
9. Hardeners, antifoggants, preservatives and color sensitizing dyes are now added.
10. The emulsion is now spread on the supporting base.
11. Storage--Sensitized photographic materials are perishable. The higher the temperature or humidity, the faster they deteriorate.

Exposed film should be processed as soon as possible. Black and white films can be kept for approximately 72 hour sat below 75 degrees before deterioration of latent image takes place.

Handling Film--This is a simple task, remember that both the emulsion and backing are easily scratched, finger printed, and spotted. Sheet films are notched to help you identify the kind of film and the emulsion side. Always handle film by the edges.

• Blue sensitive film is sensitive to blue and ultra violet. Used for copying. Not sensitive to red or green.

• Orthochromatic film is sensitive to green, blue and ultra violet. Use for special effects, copying and graphic arts printing. Not sensitive to red.

• Panchromatic film issensitive to red, green, blue, and ultra- violet, and is used more extensively in the photographic industry than any other black and white film.

• Infrared film is sensitive to ultra violet, blue, red and invisible infrared radiation.

• Reciprocity failure - This is a law rather than a fault of the film and is nota common occurrence but will happen under varied light conditions when you are required to make extremely long exposures. The easiest way to explain reciprocity failure is: one unit of light falling on an emulsion for 100 seconds does not have the same photographic effect as 100 units of light falling on the same emulsion for one second.

• Definition - The ability of a film to render good definition is dependent on graininess, resolving power, and sharpness.

• Graininess - Black and white film is composed of microscopic grains of silver which tend to clump together and form a granular pattern which will become visible when a negative give is enlarged. Generally the faster films tend to have more grain. Graininess is increased by over development and high density of the negative. Kodak divides graininess into the following categories: coarse, moderately coarse, medium, fine, very fine, and extremely fine.

• Resolving Power - The ability of an emulsion to record fine detail is referred to as resolving power. Resolution falls off greatly at high and low exposure values. Resolving power is rated by a numerical value, which is the number of lines distinguishable per millimeter when viewed through a microscope. Some examples would be: Low resolving power--55 lines per millimeter. High resolving power--96-125 L.P.M. Extremely high resolving power--above 225 L.P.M.

• Sharpness - The ability of a film to yield good edge sharpness is defined as sharpness. This means that the group should not run together. There should be a definite difference. Sharpness varies from film to film because of the following factors: emulsion thickness, thickness of the base, and the film's antihalation properties.

In order to obtain maximum definition check the following:

• Have a clean lens free from dust and fingerprints.

• Make sure the camera is in good condition and have all interior parts matte black.

• Focus camera carefully and hold it steady when taking any pictures.

• Expose for the lowest density and avoid over developing.

• Use a condenser enlarger for printing and check the enlarger lens to be sure that it is clean.

• Try to use grade 2-3 paper; 1 will ruin sharpness and 4 will show more grain.

• The slightest vibration will cause loss of definition. Remember the nearer the enlarger is to the top, the greater the chance for vibration.

Processing - The four factors in development which effect the density, contrast, and uniformity are: temperature of developer, kind of developer, developing time, and agitation.

Developers - There are many developers. Each has a specific purpose. Choose the one that best meets the needs. To avoid overworked solutions, it is best to dilute it and use it only once. The temperature of the developer is much more critical than most people realize. A deviation of one degree is enough to effect development characteristics. Immersion of film into chemicals of widely varying temperatures would result in an effect known as reticulation. Agitation must be uniform since it affects the rate of development, particularly in high densities.

Stop Bath - There are two main reasons for using an acid rinse stop bath. Stop bath stops development exactly at the correct point and it preserves the fixer solution by preventing contamination from developer.

Fixing - The bath should be clear and checked periodically. If it is not changed when yellow the silver will deposit on the print and cause stains. The fixing time is twice the clearing time, roughly 5 to 10 minutes.

Washing - Wash at cool temperatures and avoid touching film. It is soft and will scratch extremely easy. To prevent water spots, drying marks and streaks, use photo flo. This is a wetting agent to aid in drying.

Gamma refers to the measure of the contrast of a negative image as it compares to the original subject contrast. Or it can be described as the ratio of negative contrast to subject contrast. Gamma is referred to by numbers, which indicate or measure the degree of contrast to which a photographic emulsion is developed. A gamma value of 1.0 indicates that the negative contrast (tone range) is the same as that of the subject photographed. A gamma value of .6 would be considerably less contrast while 1.5 would be much more.

Gamma is often also quoted as the yardstick for the degree of development as recommended by the manufacturer. Time-temperature charts are based on scientifically determined gamma values. In a sense it can be said that negatives developed to the same gamma will have comparable tone reproduction characteristics. It is usually recommended on time-temperature charts to develop to less than 1.0 gamma. This produces a negative with slightly less contrast than the subject, which in turn will print more like the original subject matter. This is because paper emulsions tend to increase contrast.

It must be realized that the measurement of gamma is a laboratory procedure requiring the use of accurately standardized equipment and methods. Instead the purpose is to experiment with development as it affects gamma and to study the results.

There are four factors that determine gamma value of a negative image:

1. The inherent contrast of the subject matter refers to the reflecting power of parts of the subject and to the brilliancy of the lighting or lack of it.
2. The tone characteristics of the film, fast speed films are low in contrast while slow films are by nature more contrasted.
3. Development of the film emulsion. This involves the related factors of time, temperature, agitation and kind of developer used. Gamma increases as development, time, temperature and agitation increases. Also, some developers produce more contrast than others do.
4. Exposure also affects the contrast of the negative, although to a much less degree than development.

The term "latitude" as used in photography refers to the amount of under or over exposure that can be given to a film emulsion and still produces acceptable image detail for making prints. The total amount of latitude varies from one type and speed of film to another. In general, black and white film emulsions have much greater latitude than do color films.

Agitation, as it pertains to photography, is a term that describes the movement of film in the developer. This is done so as to keep a supply of fresh developer on the film surface. However, improper agitation can produce harmful effects in the negative. The purpose of this experiment is to prove the effects of under, normal and over agitation during film development.

Treatment of defective negatives

The following information will provide helpful procedures for correcting (1) thin negatives by intensification, (2) dense negatives by reduction and (3) blemishes by retouching.

There are two causes of a thin negative: (1) underexposure and (2) underdevelopment. Where there is underexposure the only thing intensification will do, will be to increase the contrast as no further detail can be produced where there was no original exposure. If the negative was underdeveloped further detail can be brought out by intensification which redevelops the exposed image.

Prepared intensifiers in powder form can be purchased and mixed according to the instructions on the package. Victor Intensifier and Kodak Chromium Intensifier are examples of these. To use follow the following procedure:

1. Fix and thoroughly wash the negative to free it of scum and stain before treatment.
2. Prepare the intensifier as directed on the package.
3. Submerge one negative at a time in the intensifier and leave for about five minutes or until sufficient detail appears in the image. Agitate thoroughly during treatment.
4. Wash for several minutes, wipe carefully and dry.

A negative that needs reducing is one that is too dense and full of contrasts. (1) over exposure and (2) cause it over development or a combination of both. This density and contrast may be so great that good printing cannot be accomplished regardless of the paper grade that is used. The thinner parts will print up before the darker areas receive any detail from exposure. It can be remedied very considerably by immersing it in the following reducer which will greatly decrease the shadows and leave the highlights as they are.

Farmer's Reducer:

Hypo solution (1 part hypo to 5 parts water) --- 8 ounces.

Potassium ferricyanide (10 per cent solution--Q.S. (Quantity Sufficient). To add Q.S. means add enough potassium ferricyanide to the hypo solution to make it a light lemon color.

1. Immerse the negative in the lemon colored solution and agitate. Add more ferricyanide solution if the negative does not appear thinner after a few minutes.
2. When the negative is reduced the required amount take it out quickly and wash or the reducing may go on and spoil the negative.

A negative that has small transparent spots in it can be spotted as follows:

1. Place the negative on a lighted board or retouching desk.
2. Clean the polished side of the negative with a safe negative cleaner.
3. Rub this side with a retouching medium in a rotary motion to give the surface a "bite" for applying touch up.
4. Touch out the pinholes by making "comma" like marks with a medium soft lead.
5. Spotone may be applied in the same manner with a small pointed brush. Work with a rotary motion and move slowly and carefully from the centers lifting off lightly at the edges of each spot.

A good black and white negative is dependent on the following variables: quality, cleanliness, density, contrast consistency, shadow detail, and highlight detail.

Quality--The quality of the negative is determined by how sharp the image is in focus. There should be detail in both the highlights and shadows. The image should not be grainier than the film will allow.

Cleanliness--The negative should be free from scratches, static markings, scum, pinholes caused from dust, fingerprints, and mottle or marks caused from unequal development. After processing, the film should be hung to dry in a place, which is free from dust.

Density--Density is determined by exposure. The longer film is exposed to light the denser it becomes. In order to determine the density of a negative, read the lowest density in a shadow area and the highest density in a highlight area. The difference between the highlight and shadow readings is the density range of a negative. This is done commercially with a machine, which is called a densitometer.

Contrast--The contrast of a negative is directly effected by development, film emulsions, various lenses, and brightness range of subject. One method of measuring contrast is by the use of gamma. Gamma is used to express contrast numerically. A gamma of .6 to 1.2 or roughly .8 is good contrast. A good way to determine the contrast of a negative is to place it (when dry) over a sheet of white paper with black printing on it. If the printing is readable through the highlights, then the negative should have good contrast.

Consistency--The ability of the photographer to record a picture on two separte sheets of film, process them at different times, and have both negatives appear identical, is a definition of consistency. Each photographer will differ in their method of processing. Such items as reading the temperature, agitation, and quickness of changing the chemicals all will vary with each photographer.

Shadow Detail--Shadow detail adds to the overall effect of the picture. Lack of shadow detail is due to underexposure, overworked developer, and flare. Flare is a non-image forming light reflected from glass or bellows. Some flare is acceptable but too much will fill in shadow detail.

Highlight Detail--The highlight is what will make a good photograph. Without a good highlight, the negative will be flat and have gray highlights. Lack of highlight detail is due to overexposure, underdevelopment, and dust or finger marked lens.

Flare would be an example of a fault, like many faults that can cross over from one category to another. It can fill in both highlights and shadows, which affects contrast.

Whenever making a critical exposure, it would be wise to bracket the exposure. Three exposures are usually enough to make sure of correct exposure. This would be one stop overexposure, estimated exposure, and one stop under exposure. A very general rule is to expose for the shadows and develop for highlights.

The ISO number assigned to each film is used to estimate the film's relative sensitivity to light. For example if all things are equal ISO 400 requires 1/2 the exposure of ISO 200. Usually the ISO number is for the minimum exposure, however the speed can vary with different light conditions, exposure, developers, agitation, and temperature. Trial exposures should be made to determine the best combination of exposure and development.

There are two different ratings:

Generally there are three different speeds of film: Slow ISO 20-80; medium ISO 100-250 and fast ISO 300-500. Each of these speeds has advantages and disadvantages. Try to get in the habit of using one speed of film and to know it. Film's sensitivity is directly effected by the size of the silver crystals. An emulsion with large crystals needs less light than an emulsion with small ones.

Fast Film Speeds - Modern films yield sharp detailed images better than ever before. These films can be pushed to higher speeds and still give fair sharpness under low light conditions, or for stopping rapid action. The problem of grain can be used to the photographer's advantage. It gives the print a texture or visual feeling. Fast films tend to produce less contrast than medium or slow speed films.

Medium Film Speeds - Medium speed films can offer some of the advantages of fast and slow films. Medium speed films are not as contrasty as slow films and do not have the grain problem of the faster films. The best condition in which to use medium speed films is under intense illumination situations. However for the future with the improvements being made on the faster films, there will be less for medium speed films.

Slow Film Speeds - The slow speed films offer the advantage of getting detail in a sunlight condition. Slow speed films can be used for large blow-ups without losing details or showing grain. They will produce higher contrast than fast or medium speed films.

Exposure Latitude--The better quality negatives usually result when film is given the least exposure. The exposure latitude is the amount that the film may be underexposed and overexposed and still produce an image with sufficient detail for printing is called exposure latitude. The latitude varies with different emulsions. Black and white film has more latitude than color film.

Confused with all the different designations for film speed? Here's what they mean: ASA, DIN, and ISO are all found on film packaging. ISO, ASA, DIN are all film speed rating systems used by the manufacturers to indicate a film's relative sensitivity to light. The higher the number, the faster or more light sensitive the film.

• The ISO numbers are determined by a formal testing procedure designed by the International Standards Organization.

• DIN (Deutsches Industrie Norm) is the German testing equivalent to ISO. Although both ISO and DIN appear on films sold in America, ISO is the preferred system here while DIN is more often used in Europe.

• ISO (International Standards Organization) is the newest designation appearing on film boxes. It is a relatively new film speed rating system and its numbers are the same as the ASA numbers. They are currently appearing together on the film but eventually ASA will be phased out in favor of ISO.

• ASA (American Standards Association) is a film speed rating system that was used by all of the American films.

• EI means Exposure Index – Which refers to a film speed rating which differs from the official speed designated by the manufacturer as ASA, DIN, or ISO. In other words, if you shoot your ISO 400 Tri-X at 800 you would refer to it as EI 800 rather than ISO 800.

The new chromogenic black-and-white films: Agfapan Vario-XL and Ilford XP1, are films, which are a fundamentally different from the conventional slow, medium, or fast films. The traditional films produce negative images that are made up of stable silver particles; the chromogenics produce images which, like color negative images, consist of dyes. The image is actually blue-black or brown rather than the usual gray, which most photographers are accustomed to with conventional films.

There are some interesting features of these films: although rated at ISO 400, this is actually a rather loose designation since they allow a very wide range of EI settings, all on the same roll, if need be: 50-1600 for XPI and 125-1600 for Vario-XL.

The acutance (sharpness) of the chromogenics is excellent even when exposing at 1600, and contrast is good throughout the shooting range. Also, grain decreases the more the film is overexposed--quite unlike the behavior of conventional films.

Are chromogenics the ultimate, do-everything films? Well, there are some drawbacks. These films are more expensive and cannot be processed in conventional black-and-white chemicals. Chromogenics must be processed like color negatives, which is a more expensive and slightly more demanding task.

Finally, dye images fade, regardless of how they're stored, and these will certainly fade just as color negatives do. Ilford claims their chromogenic negatives should last at least 50 years without significant deterioration. (Life can be extended with refrigeration.) In comparison, a properly processed and stored conventional black-and-white negative should last indefinitely.

The above-mentioned films will probably take care of most, of the needs of the photographer. However, there are other 35mm black-and-white films available for specialized applications. Kodak Recording Film 2475, is an extremely fast and very coarse grained film for shooting in low levels of existing light. It's especially useful for indoor sports photography or any place where flash cannot be used. Depending upon how it is processed, it can be exposed anywhere from EI 1000 up to 3200!

Another Kodak film to be aware of is Technical pan film. Tech pan film has an extended red panchromatic sensitivity and has extremely fine grain and extremely high resolving power. The emulsion offers a variety of film contrasts and speeds.

Once a film is chosen, stick with it until it is mastered. Avoid the temptation to try one of everything all at once; that leaves you with no valid basis for comparing the results. Once the photographer becomes familiar with all of one film's characteristics then they can branch out and try another.

When push processing film, over development is done to compensate for underexposure. Negatives that are underexposed will usually produce better looking prints with push processing than with normal processing. Keep in mind that negatives which were push processed will not produce the same level of quality as normally exposed and processed negatives. Before deciding to push process film be aware of the following facts:

• Push processing does not significantly increase the speed of any film. Increasing the development times will not put detail on the film where nothing was recorded in the camera.

• Push processing does increase film contrast, which is seen as increased separation of tones. When film is exposed in low contrast light (no shadows), the prints may be quite accep- table. When the light is contrasty (distinct shadows), the negatives may be difficult to print.

• Push processing increases graininess. Grain will be more apparent in enlargements.

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