ISO 50 slow
ISO 100, 125, 200 medium
ISO 400 fast
ISO 1600–3200 ultrafast
Medium- and slower-speed films are mostly meant for brightly lit subjects.
You will usually need fast film in dimly-lit outdoor conditions, for sports and
other action subjects (even in bright light) and almost always indoors, unless
you’re using a flash. But you also can use most fast films outdoors, even in
bright light. Ultrafast films (ISO 1600 or faster) are useful in very dim conditions,
such as at night or in clubs.
Grain. When film is developed, the silver halide crystals that were exposed to
light form small black clumps of metallic silver, called grain, that make up the
photographic image. Grain looks a little like particles of sand. You will recognize
it when you see it, for example, when you’re viewing your film through a
magnifier or looking at an enlarged print. The size of the individual clumps can
vary according to the type of film you use.
Slow- and medium-speed films (ISO 200 or lower) produce smaller particles
of silver, and are therefore called fine-grain films. Such films reproduce subject
tones smoothly and render subject detail finely and accurately. Fast-speed films
(ISO 400 and higher) use larger particles of silver to create the image. Ultrafast
How Film Records an Image
The film’s emulsion layer holds the key to understanding
how a photographic image is formed. The
emulsion contains silver halide crystals, which capture
the light projected by the lens onto the film’s
surface. Certain areas of the film receive more exposure
than other areas, since light areas of the subject
reflect more light than dark areas. For instance, a
white sweater reflects more light than blue jeans, so
more light will expose the area of the film representing
the sweater than will expose the area representing
the jeans.
When you take a picture, an image of your subject
forms as an invisible pattern of altered silver
halide particles in the emulsion. This is called a latent image. Chemical development converts the
film’s exposed silver halides to black particles of
metallic silver, making the image visible.
Film development takes place in proportion to
exposure. In other words, when film is exposed, a lot
of silver forms in the brighter areas of the subject and
renders those areas dark on the film; relatively little
silver forms in darker areas, which renders these
areas as light on the film. Thus your developed film
contains a tonally reversed image—a negative. The
light areas of the original scene are dark and the dark
areas of the scene are light. Making a print from the
negative reverses the image to produce a positive,
correctly representing the tones of the subject.
films (ISO 1600 and higher) are sometimes called coarse-grain films, or simply
grainy, and reproduce image tones and details more roughly and with less
subtlety. ISO 400 films are generally considered medium-to-fairly-fine-grain.
The choice of film, with its inherent grain characteristics, is one of the most
important controls you have over the final look of your work. Some subjects,
perhaps a lush landscape or an elegant flower, may look best when photographed
with a fine-grain film that reproduces the scene with smooth, rich
detail. Other subjects, such as a gritty urban scene, may feel more real when
photographed with grainier (coarse-grain) film. It’s very much a matter of individual
preference.
Note that film type is only one factor that determines grain. Other factors
include film exposure, film development, and print size. Even film speed isn’t a
totally reliable gauge of graininess. An ISO 400 film from one manufacturer
may produce finer or coarser grain than an ISO 400 film from another. Some
manufacturers even offer more than one film choice with the same ISO, but
different grain characteristics.
Tones. A black-and-white photograph is rarely just black and white. Instead, it
is made up of a range of shades—blacks, grays, and whites. These shades are
called tones, and the variety of tones from dark to light contained in an image
is called the tonal range. For instance, a photograph of a chess board might
have a limited tonal range, since it consists mostly of blacks and whites; a
photograph of the surface of a lake would have a much longer tonal range,
since it is made up of dozens of subtly different values ranging from black to
gray to white.
Some films are capable of reproducing more of a subject’s tones than others.
As a general rule, slower films, such as ISO 50 and 100, reproduce more tones
than faster films, such as ISO 1600 or 3200; the fine grain of slow-speed films
captures more information to better render subtle differences. Note that several
other factors can play a large role in tonal range, including the inherent tonal
characteristics of the subject, film format, and film exposure and development.
Contrast. Contrast refers to the relative difference between dark and light tones
in the original subject or in the negative and print that represent the subject. All
other things being equal, some films inherently produce more contrast than
others. Higher contrast films produce dense blacks and bright whites, with few
shades of gray, while lower contrast films produce more grays and a subtler
transition from the darkest tones to the lightest.
As with other film characteristics, contrast is a function of several factors
other than the film you use. The original subject lighting is critical, as is film
exposure and development; when printing, you can use different papers and/or
colored filters to vary the image contrast.
Film format refers to the size of the film used by a particular camera. Over the
years, there have been many different film formats, but today they can be
generally classified as follows:
35mm
medium format
large format
35mm. By far, the most common film format is 35mm, which measures 35
millimeters wide. It is packaged in rolls that produce 12, 24, or 36 exposures;
the narrow strip of film is coiled around a plastic spool and encased in a metal
cassette for protection and to keep light out. You also can buy some types of
35mm films in longer rolls, known as bulk film, for reloading into reusable
cassettes.
Because 35mm is a relatively small format, most of the cameras that use it
also are small. This makes it an ideal choice for spontaneous and action work,
such as candid portraits, photojournalism, and sports photography.
Thirty-five millimeter cameras almost always produce images measuring
24 x 36 mm (a little less than 1" x 11⁄2"), but sometimes they produce different
sizes and shapes depending on the rectangular opening in the back of the
camera body. The most common alternative size is called panoramic, because it
provides a wide panorama of a scene. In most models, the camera’s manufacturer
achieves this wider view by masking out the top and bottom of the 35mm
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