Forensic Dentistry, Second Edition

214 Forensic dentistry

11.7 Film-Based Photography

Film manufacturers have designed photographic films that record light
wavelengths from 250 to 700 nm. Special infrared films are available that can
record photographs captured in light from 250 to 900 nm.32,34 Choosing the
proper film is critical for successfully recording the detail of an injury. The
film must be sensitive to the wavelength of light being used to photograph
the injury or no image will appear when the film is developed. There are
many quality photographic negative films manufactured, in both color and
black and white. Table 11.2 suggests some readily available films, processing
techniques, and their potential uses in forensic photography.
In addition to the photosensitivity range of the film, the correct film
speed must also be determined. Films come with a rating, referred to as the
ASA/ISO number, which serves as an indicator of the amount of light energy
necessary to properly expose the film. The higher the ASA/ISO number, the
faster the film; in other words, less light is needed to expose an image. Films
with high speed ratings (ASA 1600 or 3200) require very little light energy
to expose, but caution must be exercised. The higher the ASA/ISO number,
the lower the grain density on the film where the image is recorded, which
translates into less versatility during enlarging. Large-grain fast films tend
to produce prints that appear to lose focal sharpness and detail as they are
enlarged toward their normal limits, i.e., life size or 1:1.
Just as there are good and bad attributes for high-speed films,
slower-speed films can also have limitations. Using a film speed that is too
slow for the amount of available light will result in an underexposed picture
that may also lack clarity and detail. There are some situations where the
photographer does need to underexpose for better detail, particularly dur-
ing fluorescent photography. This will be discussed later in Section 11.9. The

Table 11.2 Summary of Nonvisible Light Techniques

Ultraviolet Infrared ALI

ASA/ISO range ASA 100–400 ASA 25–64 ISO 100–400
f-stop range f-4.5 through f-11 f-4.5 through f- 22 f-4.5 through f- 11
Shutter speed range 1/90" through 1/125" 1/125" through 2" 1/60" through 2"
Filter (on lens) Kodak Wratten 18A
(film photography),^25
Baader Venus UV filter
(digital photography)

Kodak 87 gel or

glass^25

Varies with subject
matter. For injuries
on skin, #15 yellow
gel^25
Illumination
wavelength (nm)

200–390 nm 700–960 nm Varies with subject.
For bites and other
injuries, 450 nm.
Films Kodak TMAX 400
Kodak PhysX 125

Kodak Highspeed

Infrared, ISO 100

Fuji Reala 100