Obliqueillumination microscopy

Obliquecontrast

Since most laboratory photography is made with steady burning lights (quartz lamps, photoflood lamps, fluorescent lamps, etc.) it is relatively easy to choose the best lighting method for photographing a specific item of evidence. All you need to do is try different lighting methods while looking in the camera's viewfinder, and select the method that gives the best results. The following lighting methods are effective for photographing various evidence subjects.

Bounce lighting uses light bounced off a white or reflective surface. The bounce surface may be positioned at different locations (above or to one side of the subject) to create the desired effect. This usually produces even non-glare lighting with low contrast.

Oblique lighting is commonly used when photographing impressions, tool marks and certain types of fingerprints. A very low oblique angle of lighting can be used to photograph dusty footwear impressions and indented writing.

Oblique lightexample

Transmitted lighting is used for photographing transparent or translucent subjects. It is effective in photographing evidence such as a fingerprint on a drinking glass.

Direct reflective lighting is used to minimize shadows within the evidence. However, this method creates very high contrast and does not show the dimensional shape or texture of the evidence. Also, the light source may need to be diffused to prevent hot spots.

Obliqueillumination examination

Transmitted lighting uses light that shines through the evidence toward the camera's lens. The background becomes shadow-free. The angle of the transmitted lighting can be adjusted from 90-degrees to 45-degrees for the desired effect.

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45-degree lighting uses one or more lights positioned at 45-degree angles. If only one light is used, a white or silver reflector can be placed on the opposite side of the evidence to reflect some of the light back toward the evidence, reducing shadows.

Diffused lighting uses an opaque material placed between the light source and the subject to soften the light. This usually results in even lighting with reduced reflections and hot spots. The opaque material can be as simple as a section of a white bed sheet or an empty water bottle, or can be a commercial device designed for laboratory photography.

What is obliquelighting in Forensic Science

45-degree lighting is used for photographing the average item of evidence where the objective is to show the item's shape and size.

Oblique lighting uses a light source positioned at a low angle. Oblique lighting is usually used to show detail by creating shadows on the surface of the evidence.

Oblique lightphotography

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Transmitted lighting

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The principal purpose of this Guide is to provide an investigative outline of the tasks that should be considered at every explosion scene. They will ensure that proper procedures are used to locate, identify, collect, and preserve valuable evidence so that it can be examined to produce the most useful and effective information-best practices. This Guide was designed to apply to explosion and bombing scene investigations, from highly complex and visible cases, such as the bombing of the Alfred P. Murrah Federal Building in Oklahoma City, to those that attract less attention and fewer resources but may be just as complex for the investigator.

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In direct reflective lighting the light is reflected directly off the subject into the lens. This is done by placing the subject at a 10-degree angle from the lens to film plane and placing the light source at a 10-degree angle from the subject. The light source reflects at a 20-degree angle into the lens.

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