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Coaxial Lighting for Forensic Photography

Machine Vision

t has been said that if one can see something, then that "something" can be photographed. Once seen, the photographer can then use his expertise to select the proper camera, lens and film combinations required to capture a usable image.

Lighting of the subject is one of the most crucial, yet overlooked aspects leading to it being accurately recorded.

In too many cases the photographer is satisfied to fire away at that elusive evidence using a camera mounted electronic flash, but shocked to find the subject of his efforts absent or woefully inadequate once the film has been developed.

Of the countless surfaces requiring accurate imaging, those that are highly reflective, such as plastic, glass, mirrors and polished metal are some of the most difficult to accurately record. Imaging of such surfaces requires specialized lighting techniques, often combined with unique camera positioning only possible through the use of cumbersome large-format view cameras capable of offset film and lens planes.

While the view camera is a luxury that few scenes of crime units are blessed with, it is safe to say that the "view video camera " is a device unheard of in the machine vision arena.

Fortunately, a lighting technique exists which allows us to visualize detail on these difficult surfaces using relatively simple camera equipment, both still and video.

This technique is known as coaxial lighting, and has proven to be an effective addition to the list of tools available to the Crime Scene Investigator when faced with the task of visualizing and photographing difficult fingerprints found on reflective surfaces.

Simply stated,coaxial lighting is the illumination of the subject from the precise direction of the imaging lens, either through the lens or with a beamsplitter in front of the lens.

For a short flash movie demonstrating the application of coaxial lighting, click HERE.

It has been asked if a ring light can perform the same function.
This is why it won't work.


Here is a brief lesson on the proper method of positioning your subject for optimal results.