Films, Continued
Sheet or cut
film
Video disks
Film
characteristics
Emulsion
sensitivity
Sheet or cut film is made in a variety of sizes from 4 by 5 to 11 by 14 inches
and larger. Sheet film does not have a paper backing and must be loaded and
removed from film holders in total darkness. Most sheet films have notches
in one ‘edge of the film to identify film type and emulsion side when in the
dark. Emulsion to emulsion contact or emulsion toward the copy produces
the sharpest images. The emulsion is toward you when the notches are on
the top edge, upper-right corner of the film or the bottom right edge, lower-
right corner of the film. For sheet films without notches, the emulsion side
of the film can be identified by its lighter color when viewed under a
safelight. If the emulsion side of the film must be identified in total
darkness, wet your lips and place the edge of the film between them. The
emulsion side of the film will stick to one of your moistened lips.
Most electronic cameras use compact, 2-inch, still-video floppy disks to
record images as magnetic impulses. Video disks do not contain emulsions
or a base. The camera and the printer determine whether an image is black
and white or color. Pictures are recorded in either the frame or field mode in
the camera. The frame mode records each image on two tracks. Twenty-
five images fit on one disk in the frame mode. In the field mode, each image
records on one track so 50 images fit on one disk. The quality of frame-
recorded images is superior to that of the field-recorded photograph. Floppy
disks used in electronic imaging may be reused endlessly. No chemicals or
darkroom techniques are required. Once captured on disk, an image can be
transmitted over telephone lines, edited, and printed - all under normal
room light.
Film characteristics are determined by the films degree of sensitivity to
light, response to various colors of light (color or spectral sensitivity),
contrast, exposure latitude, emulsion latitude, and emulsion definition. The
characteristics and use of black-and-white films depend largely on the
construction of the emulsion.
Film emulsions are very sensitive to low levels of light. The light causes
invisible changes to the emulsion. These changes or images are called latent
images. Latent images become visible after chemical development. The
property of a film emulsion to respond to light is termed film speed.
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