Oblique Lighting with the ALS
by Hayden B. Baldwin


Photographing a footwear impression in dust is sometimes difficult, especially if the dustprint is on a highly reflective surface, such as a gelatin lift or mylar from an electrostatic dustprint lift. Either reflective surface will cause glare back into the camera from the light source. However by using the ALS, a beam of light can be positioned so the light is parallel and just above the reflective surface. This lighting technique has proven successful in photographing these difficult surfaces. No camera reflections, no light flares, no hot spots - just even lighting for a photograph suitable for comparison to the suspected footwear.

This lighting technique can be used on any surface, not just highly reflective surfaces. Footwear patterns found on concrete, wood floors, tiled floors or any surface that oblique lighting identifies an impression. The use of the ALS should not be confined to just oblique lighting for footwear but also for lighting any dust impression, such as a finger or palm print, fabric impressions or to photograph the dust to show the disturbance or lack of disturbance at the crime scene.

Exposure time has been approximately 12 seconds at F4 with 100 ISO film. Exposure will depend on the intensity of the light source and the distance between the light source and the object to be photographed.

The light source must be held almost parallel or you will have uneven illumination of the object you are attempting to photograph.

CAUTION:  The white light frequency on the ALS should not be used for more then 45 seconds with the fiber optic cord attached. The power output may burn the fiber optic cord. However if you are using a liquid fiber optic cord no harm will be done. The other light frequencies will not effect the fiber optic cord.