Film speed appears on every roll of film and is an industry-rated standard.
The standard is set by the International Standards Organization (ISO). Film
speed, sometimes referred to as film sensitivity, indicates the sensitivity of
the film emulsion to record latent images of light. Film speed may be fast or
slow. Selection of a film speed requires a knowledge of film characteristics,
lighting situations, and potential compromises.
FAST FILM: Film considered fast is film that requires less light for
exposure. These are the low-light film speeds of ISO 400 and higher. Image
resolution is good in small prints; however, pronounced graininess appears in
enlargements. Some of the very fast films, ISO 1000 and faster, need very
little light and an extremely short exposure time, making them more desirable
for dimly lit auditoriums and difficult to handle in daylight situations.
SLOW FILM: Slow film requires more light or longer exposure times to
record an image. Slow films, such as ISO 25, have very fine grain that
remains fine even in enlargements. These films are ideal for a controlled
Sometimes a photo lab is not available to produce duplicates of slides or
transparencies. The DM is able to duplicate slides using a slide duplicator
that attaches to the front of a camera body much as a lens does. The
duplication process allows the DM an opportunity to correct minor exposure
errors and perform limited cropping of the original slide. The light meter in
the camera can meter exposure. Transparencies, placed on a light table or
the illuminated copyboard of a process camera, can be re-photographed with
a 35mm camera and slide film.