Demonstration of Coaxial Lighting
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Imaging Difficult Subjects on Difficult Surfaces

This image demonstrates the value of coaxial lighting in visualizing a fingerprint on the surface of a mirror. The fingerprint is in its"as left" state. No forms of development have been employed.

A difuse light source has been employed, and the coaxial path followed by the light has resulted in a uniform bright field reflection directed through the lens and onto the film plane. The only interruption of the bright field is in the form of the ridge detail present on the surface of the mirror. Since the ridge detail prevents a direct reflection of the coaxial light onto the film, it appears dark to the camera.

The resulting image is that of a dark fingerprint on a light background. The use of coaxial lighting allows the location of the camera directly above the mirror, minimizing the problem of offset ridge reflections

This subject is very similar to the silver plates used with iodine fuming when examining cadavers for fingerprints.

photograph of fingerprint on mirror

Another shiny surface is illustrated. The data side of this compact disk bears a fingerprint. Again, the fingerprint has not been processed in any way.

This lighting technique is beneficial in cases involving optical storage medium where the use of possibly destructive development techniques is not an option.

photograph of fingerprint on cd photograph of fingerprint on cd

This photograph illustrates the non-data side of a compact disk bearing a fingerprint.

Since the entire surface is somewhat matte in texture, the direct specular reflection associated with a mirror-like surface is not present. The fingerprint can be visualized and recorded by "huffing" on the surface of the disk, introducing a layer of condensation and thus, further altering the surface texture.

photograph of fingerprint on cd photograph of fingerprint on cd

An impression on a piece of black "Plexiglass".

Another unprocessed article, relying on the difference in reflective qualities between the fingerprint and the substrate.

As demonstrated, even the jet black sustrate appears white due to its highly reflective surface texture.

photograph of fingerprint on plexiglass photograph of fingerprint on plexiglass

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

 

 

 

photograph of fingerprint on mirror