Abstract
Abstract
Non-uniform illumination originates from (1) non-uniform transmission of light by model and polariscope elements, (2) diffraction and obstruction of light by the edges of elements and camera shutter, and (3) internal reflections of light from lenses and covering glasses. Effects appear as (1) a locally non-uniform background intensity distribution on the viewing screen or camera film, (2) a peripheral zone of generally reduced intensity, and (3) a bright central spot.
This paper shows how local non-uniformities can be detected by photography. The peripheral zone may be avoided by use of a reduced size of field. Remedies for the deleterious bright spot may include a suitably chosen distance between first field lens and model, a small camera aperture and, in extereme cases, a translucent screen between light source and first field lens.
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