NCJ Number
138347
Journal
Journal of Forensic Sciences Volume: 37 Issue: 4 Dated: (July 1992) Pages: 1084-1095
Date Published
1992
Length
12 pages
Annotation
Photographic demonstrative evidence can be valuable in understanding visibility issues involved in nighttime crime scenes, but several criteria must be satisfied to ensure that results accurately represent visibility conditions.
Abstract
The forensic nighttime photography technique involves the use of a slow-speed slide film having substantial linearity, such that the contrast rendition of the crime scene is reasonably good. The slide is then projected, and neutral density filters are used to reduce the output from the projector so that the viewed image has a luminescence comparable to that of the original scene. The use of a slide duplicating film results in good contrast fidelity and an extended luminance range. With appropriate calibration, the resulting slides can be projected with neutral density filters used to reduce projector output, such that the screen image's luminance is equal to the luminance that would have existed at the scene. This is particularly important because vision thresholds heavily depend on adaptation level. Angular fidelity is achieved by calculating the viewing distance to give all crime scene objects their true angular size. A procedure is described that permits a numerical evaluation of the fidelity of projected images with respect to threshold observation of crime scene detail. This procedure may also be useful in the exclusion of nighttime photographs that do not meet the criteria. 7 references, 1 table, and 6 figures