Films, Continued
Spectral
sensitivity
(Continued)
ORTHOCHROMATIC: Orthochromatic films are sensitive to ultraviolet
radiation, violet, blue, and green light. The emulsion provides
approximately correct reproductions of blue and green objects in
corresponding tones of grey in daylight or tungsten light.
Used primarily for
copy work and graphic arts photography, orthochromatic film trade names
usually contain the word “ortho.” Ortho-type films may be used as
continuous-tone or halftone (line) film.
PANCHROMATIC: Panchromatic films are sensitive to UV radiation,
violet, blue, green, and red light. Panchromatic films are used for copy
work, portraiture, and general photography. These films have only one ISO
speed.
INFRARED: Infrared film emulsions are sensitive to UV radiation, violet,
and blue light, with little sensitivity toward yellow-green light. Sensitivity to
red and infrared light is heightened. Infrared film is used for aerial and
medical photography. Since infrared radiation does not focus at the same
point as visible light, a lens focus adjustment is necessary for critical
focusing. Most lenses have a calibrated IR-focusing position on the depth-of-
field scale marked by a small dot or the letter “R” in red.
Figure 7-22 shows the calibrated focus adjustment required to compensate for
infrared film.
Figure 7-22.—The calibrated focus adjustment
indicator for infrared films.
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