Films
Introduction
Selection of an appropriate film requires knowledge of film characteristics,
lighting situations, and potential compromises. There are many types of
conventional films to choose from as well as video disks.
Film
Film is an emulsion of light-sensitive silver halide salts on a translucent or
transparent acetate base.
When struck by light, the emulsion hardens and
deforms recording a latent or invisible image. Chemical additives in the
emulsion determine the range or wavelength of light to which the film
responds. The image visibly appears only after chemical development.
Black-and -
white fiiii
composition
Black-and-white film is a light-sensitive emulsion on a transparent or opaque
base used to photograph reversals (positive) or negative images. In addition
to the emulsion and the base, there are three additional layers of substances
that perform special functions. Overcoating, antihalation backing, and
noncurl coating complete the five component parts of black-and-white
photographic film.
EMULSION: The emulsion contains light-sensitive silver salts called silver
halides. Silver halides react to ultraviolet (UV) radiation, violet, and blue
light only. They can be made sensitive to other colors of light and infrared
radiation (IR) by the addition of dyes. A gelatin evenly disperses the silver
halides and dyes onto a base.
BASE: The film base holds or supports the emulsion.
OVERCOATING:
Overcoating is a clear layer of gelatin that protects film
from friction, scratches, or abrasion. The overcoating is sometimes called
the antiabrasion layer.
ANTIHALATION BACKING: The antihalation backing prevents light from
reflecting from the base back into the emulsion.
NONCURL COATING: The noncurl coating is a hardened gelatin applied to
the back of the film that prevents the film from curling during the drying
process.
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