Abstract

An “ideal method” of illumination is advanced with specific means for its production in metallography. It is shown that it is deleterious to ocular perception and photography to illuminate with rays parallel or even nearly parallel to the line joining the object and the eye or the camera, not only for perception with the unaided eye but through the microscope. In metal microscopy axial light is deleterious because it produces an inferior image of lower resolution and definition and it also neutralizes the shading effect of oblique light thus rendering many details invisible by obliterating relief. Therefore, axial light should be eliminated and selected portions of the remaining hollow cone manipulated as described. Several types of apparatus are briefly discussed and an improved device is described. The article is illustrated by diagrams and by studies of grain structure in a solid solution.

© 1927 Optical Society of America

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