INFRARED PHOTOGRAPHY
Infrared photography is the recording of images formed by infrared radiation. Because infrared radiation is invisible, some special techniques may be needed. But, in general, most of the commonly required methods are as simple as those of ordinary photography.
Uses In Law Enforcement
1. Questioned documents.
2. Aerial photography.
a. Infrared photography can enhance the contrast of the
terrain.
b. Coniferous (darker) and deciduous (lighter) growth is
differentiated.
3. Surveillance photography.
4. Detection of gunshot-powder burns, stains and irregularities in cloth.
5. Detection of certain types of secret writings.
Equipment
1. Camera
a. Almost any camera. The 35mm camera is most convenient in
most cases.
2. Lenses
a. Most good lenses can be used in infrared photography.
b. It is helpful if the lens has an infrared focusing scale.
Film
1. Black-and-White Infrared Film
a. Records infrared luminescence from subjects.
b. Requires an infrared filter on the camera lens. Try a Kodak
Wratten Filter #87.
2. Color Infrared Film
a. Not usually a good choice for law enforcement use. Color infrared film
is a "false color" film. It is sensitive to blue
radiation in all its film layers so a yellow filter
must be used to filter out the blue.
b. Color infrared film can be used to emphasize differences between objects
that are visually quite similar. Color
infrared-sensitive films emphasize differences
in infrared reflectance.
3. Loading Film
a. Infrared film is sensitive to heat and should be refrigerated.
Allow sufficient time for the film to reach room temperature
before opening the package.
b. Kodak High Speed Infrared Film must be loaded and unloaded
in total darkness because the felt-lined slots of the
magazines are not "light-tight" to infrared. Both exposed and
unexposed film can be safely stored in the sealed film
container.
Lighting
1. Use tungsten lamps or electronic flash units for black-and-white infrared
photography.
2. Use electronic flash illumination for color infrared photography. Other
light sources (except daylight) require special
filtering.
Exposure
1. Exposure is determined by test shots.
2. Using Kodak High Speed Infrared Film with a Kodak Wratten Filter #87,
try an ISO 25 for daylight and an ISO 64 for tungsten lighting.
Focusing
1. Focus in a normal manner without the filter in place.
2. The distance that appears opposite the normal index mark on the lens should
then be moved to the red (infrared) index mark. This
will usually result in a lengthening of the lens.
3. Replace the filter for the exposure.
References
1. Kodak Applied Infrared Photography, 1981 (M-28)
2. Kodak Using Photography to Preserve Evidence, 1982 (M-2)
3. Kodak Photographic Surveillance Techniques for Law Enforcement Agencies,
1976 (M-8)