Tracks and stars in nuclear track plates are usually found by ordinary bright-field microscope procedures affording limited field of view and requiring continual focusing up and down. Standard dark-field illumination schemes fail due to background scattering by fog grains. A rotating-azimuth, planar, dark-field, illumination scheme has been developed which provides sufficient contrast so that low magnification (50 to 100 times) may be used. The field of view is thereby increased to 2 to 4 mm and the depth of field becomes comparable to the total thickness of the emulsion.
E. H. LAND, G. BIRD, and W. A. SHURCLIFF, "Detection of Tracks and Stars in Nuclear Track Plates," J. Opt. Soc. Am. 40, 61-62 (1950)