Bong S. Eliab
School of Arts and Sciences
Ateneo de Davao University
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Film consists of a series of light-sensitive chemicals on top of a layer of acetate. These chemicals change at two critical times: during exposure and processing.
Films can be divided into two types, indicated by the suffix on the film box: -chrome (slide film or reversal film, which can be made into high-quality prints/enlargements) or -color (print film, which includes a orange-colored negative in the case of color film, from which a color print is made; black and white film is made up of a black and white negative from which black and white prints are made). The higher the number on the box, the more sensitive the film. This number is standardized worldwide. Thus, ISO (International Standard Organization) 400 film is more sensitive to light than ISO 100 film. (Previously, ASA [American Standards Association] was used in the United States and DIN in Europe.) Thus, photographers use high-ISO (high-speed) film for low-light situations. Why not use high-speed film all the time? Unfortunately, higher-speed film is grainier. Larger film crystals are more sensitive to light, but the clumping of these crystals (grain) shows as dots, creating a kind of "speckled" effect in large enlargements (11"x14" or greater).
(FYI-This will not be on any tests) Color film is made possible because the continuous spectrum that makes up white light can be analyzed into three equally spaced wavelengths: red, green and blue. Color film has three layers of emulsion, each layer sensitive to red, green or blue. Slide and print film are essentially the same; the difference occurs during processing; after the negative images have been processed, the film is briefly exposed (either chemically or with light) so that the silver compounds that had remained untouched now form reverse positive images. A second color development is then given. During this stage, the developer oxidizes and combines with other compounds in the emulsions to produce complementary colored dyes in the positive areas of each layer. At this stage, the three layers of film each contain a silver negative image (which is not needed) and a positive color image. After the silver is bleached out, three complementary color images are left in the layers which, when held against the light, give the effect of the original subject colors.
Your eye/brain automatically compensates for differences in color. Film does not. The colors of available light vary greatly. Color "temperature," as this is known, is measured by degrees Kelvin. Professional photographers concerned about precise color temperature--especially in the studio--will use a color meter to measure this color. Lower color temperatures are associated with longer, redder wavelengths, the higher ones with shorter wavelengths that are associated with blue. On the Kelvin scale, candlelight measures at about 2,000 degrees K., most table lamps at about 2500 degrees K., photoflood lamps are around 3200 K., and noon daylight is about 5400 K. Flash is color-balanced for noon daylight.
Of course, outdoor daylight conditions vary widely. Sunset and early-morning
photographs will have a strong red/orange cast as light rays have to pass through a large
body of atmosphere and this scatters the blue and ultra-violet wavelengths. Alpenglow is
even more reddish because of atmospheric layers. Shadows, especially at noon, have a
bluish cast, though your eye perceives them as gray. Smoke and pollution give a reddish
cast. On overcast days, light is more blue.
Manufacturers try to help with this color balance problem by making two different kinds of film: TUNGSTEN and DAYLIGHT films. Tungsten films are calibrated to provide natural colors in many artificially lit situations, such as stage shows. However, even table lamps will often be too "orange" for tungsten film. Tungsten film is indicated by a large "T" on the film box and canister. Daylight film, which accounts for nearly all film made today, works well outdoors and with flash.. Fluorescent light provides a special challenge. Photographs made under fluorescent light can vary from green to magenta. (Please refer to the section on filters for more information.)
You can compensate for color balance problems by using corrective color filters, which consist of colored glass that usually mounts on the front of your camera lens. For example, you can "cool" tungsten lighting so that daylight film will record it more as your eye/brain sees it by using an 80A filter. However, this is approximate since tungsten light varies so greatly. And such a filter will cause you to lose 2 f-stops of light. Filters are covered in more detail in another hand-out.
In outdoor photography, it's fun to mix the different sources of light and not worry too much about color balance. Let your sunsets be really orange. Combine bluish early-evening light with candlelight or firelight, for example. Daylight and tungsten film will render strikingly different results of such mixed-light scenes.
Films are designed to work over a limited range of exposure times. Color balance and exposure can shift at extremely slow or fast speeds. This is called reciprocity failure. Most daylight films are designed to be used at between 1/10 to 1/1000 of a second. At speeds beyond these boundaries, under-exposure, color shift and contrast problems can occur. Bracketing can compensate for exposure, and filtration and custom processing can correct for color balance and contrast.
Sometimes you don't have enough available light for a given photographic situation. Perhaps you're photographing wild animals at dusk. All you have with you is ISO 100 film. You can set your ISO dial on your camera to 200 or even 400 (occasionally, photographers have been known to even set their ISOs to 800 or 1600) and still get an acceptable image. Be sure to mark your film canister with this new setting, and when you take your film to a CUSTOM processor, indicate that the film has been shot at this new ISO. The processor will adjust for this film "pushing," and charge you an additional fee. Your film quality will not be quite as good as if you'd exposed the film at its optimum ISO, but you will have an image. Similarly, you can "pull" film, shooting the film at a lower ISO than recommended.
For many years Eastman Kodak was the leader in film manufacturing. Kodak's fabulous film, Kodachrome, debuted in 1935 and remained the standard for decades. Kodachrome transparencies made 50 years ago still retain their beautiful colors. Kodachrome provides excellent sharpness and "real" color nuance. In the 1970s Kodak processing changed and the film lost much of its archival quality, though longevity has increased since then. Another Kodak film, Ektachrome, has long been popular because processing (E-6) is a relatively simple and can be done by most home darkroom aficionados. Early Ektachrome suffered from color fidelity and poor longevity. In the last 10 years or so, Fuji film has come to dominate the chrome market. Fujichrome film provides super-saturated colors, which means the colors are more brilliant than real life. Publishers love Fuji films because they make such brilliant color reproductions. The most brilliant of Fuji films is called Velvia; Velvia is as sharp as Kodachrome 25 and has become a favorite of landscape photographers and many professionals. Velvia must be used carefully; contrast can be a problem in sunlit landscapes. Velvia is also more expensive. Kodak has answered the Fuji challenge with its new saturated Ektachromes.
Each kind of film produces different results. For typical outdoor photography scenes in daylight conditions, choose one kind of film and stick with it for awhile. You'll learn to "see" as your chosen film sees--predicting your results.
However, only a small minority of photographers use slide film, in spite of its superior quality. Why? The tolerances of slide film are far tighter than those of print film. Thus, for everyday, family photos, go ahead and shoot print film. If prints from negatives come out too light or too dark, be aware that a custom lab can usually correct for machine processing mistakes.
Professional Vs. Amateur Film
Camera magazine ads and better camera stores make available "pro" film? "Amateur" films are designed to function optimally even after a given unrefrigerated shelf-life time. After this time, color-balance problems-typically magenta shifts-occur. ISOs and other factors listed below are not precisely calibrated in amateur films. Today's amateur films are of such quality that these factors are not a big problem. In the field, amateur films are often preferable because they don't require refrigeration.
Why use pro film? Professional film, which is more expensive, is the same as amateur film, but it is selected for its tighter tolerances in color balance, contrast and film speed. Pro films have the seven following characteristics: (1) Refrigerated storage requirements; (2) Special color distinctions; (3) Contrast design differences; (4) Altered spectral sensitivity (response to various light sources); (5) Push/pull characteristics (combined exposure and development alternatives); (6) Emulsion design variations; (7) Larger-format availability. Pros typically buy several "bricks" (20-roll packages) of pro film at the same time, all with the same emulsion number, and stick the film in the freezer. This way they can exactly predict color and exposure in a given roll of film.
Syllabus | Notes | Papers | Projects
All Rights Reserved 2001
Ateneo de Davao University
10 June 2002