Coaxial Lighting for Forensic Photography
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The Equipment

The equipment necessary to employ coaxial lighting for image visualization and recording consists of a beam splitter, used to direct light from various sources toward the subject at the proper angle of attack, and light sources consisting of both diffuse and directed-output types.

Since the beam splitter allows 50 to 60% of the source light to reach the subject, and only 50 to 60% of that light to reach the camera lens, intense light sources are required in order to allow for reasonable exposure times.

 

Beam Splitter

The beam splitter I construct is geared toward use by the Identification Community. It is larger than most commercially available units.

This unit is constructed of extruded aluminum, built to withstand severe field service. A standard tripod mounting fixture is incorporated on the housing to allow for ease of setup on non-horizontal surfaces. The optical element is easily removed for cleaning or replacement, should that be necessary, even in the field.

With a 7cm round aperture, the unit is capable of illuminating fingerprint clusters and other larger objects allowing for single exposure recording.

This unit can be used with various light sources, many of which are probably present within your unit. I would recommend having both the directed-beam and diffuse lighting options available. Although diffuse lighting is recommended for use with the coaxial beam splitter, certain subjects will show marked improvement in definition with the use of a directed-beam light source. High intensity fiber optic illuminators seem to be the most useful sources of directed-beam light, since minute changes in light direction can easily be made.

 

coaxial prism
coaxial prism
coaxial prism

Diffuse Lighting Unit

 

This lighting unit is constructed specifically for use with the coaxial beam splitter.

 

The unit is constructed from the same extruded aluminum as the beam splitter and features secure, slip on fastening to the unit.

 

Utilizing LED technology, it provides high intensity white light with an even, diffuse output. The unit produces very little heat, has an operating life in excess of 10,000 hours and can be operated using the included A/C adapter. The source power requirement is 100-240 vac, allowing the unit to operate globally. An optional battery pack will soon be available.

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

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