Forensic Dentistry, Second Edition

222 Forensic dentistry

Fluorescent photography is best accomplished successfully in complete
darkness, where all other sources of light are eliminated. One can imagine the
difficulty in setting up and capturing this kind of photograph, especially when
the exposure times can range up to 2 to 4 seconds in length and the subject is
alive and moving. A high ISO setting and very bright alternate light source can
maximize successful imaging. For weaker lights and low ISO settings, use of a
tripod-mounted camera is recommended. The light source can be handheld to
illuminate the injury from different angles. Experience has shown that slightly
underexposing one to two f-stops will produce better results than the actual
metered exposure. This is true because during longer exposures, even the fluo-
rescent light coming back to the camera is still bright enough to wash out some
of the fine detail in the injury at the metered “ correct” exposure factor.
Several variables can influence the photographic protocol and param-
eters of exposure. Skin color (amount of melanin), skin thickness, wound
healing response, light intensity, film speed, and location of the injury are but
a few factors that affect the exposure times. Thick skin as found on the palm
of the hand and sole of the foot fluoresces more than the thin skin cover-
ing the face. Darkly pigmented skin will require longer exposure times than
lighter skin because more light is absorbed by the melanin pigmentation of
the darker skin. Persons who bruise easily, such as the elderly, will produce
injuries that may require shorter exposure times due to the thinness of the
skin, but one can also expect longer exposures when greater hemorrhaging
occurs beneath the skin since the blood absorbs light.

11.10 Nonvisible Light Photography

The photographic requirements for recording injuries using nonvisible light
become somewhat more complex. The appearance of the injury using non-
visible light illumination cannot be seen by the naked eye. Therefore, special
techniques must be employed to record the injury. Once recorded, the image
must then be converted to a media from which it can be visualized. This
would include photographic paper for film or a computer monitor for digital.
Just as in ALI, these techniques require that bandpass filters be used. They
are placed between the injury and the film or digital sensor, usually on the
front of the lens of the camera. The filters allow only the selected wavelengths
of light to pass to the film or digital sensor. It is important that several factors
be considered when attempting to photograph injuries in nonvisible light
(Figures 11.21 to 11.26).
For film-based nonvisible light photography, one must consider the type
of film being used. The film’s photoemulsion must be sensitive to the light
wavelength the filter is allowing it to “see.” Additionally, the light source
must emit the appropriate wavelength and be strong enough to expose the