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Back to Photogallery - - Click on images for a larger view and more information - - Dispersion Staining, Objective Stop In the 1950's Yu. A. Cherkasov began working with optical screens at the objective back focal plane to improve on the techniques developed by Wright. He refered to this technique as Focal Screening. His work was first published in English in 1960 (Internation Geological Review, vol.2). This technique was further developed and promoted by Walter McCrone and K. M. Brown of McCrone Research Institute in the 1960's and 1970's. This is the most common form of dispersion staining used today, though not always the most appropriate. It severely impairs image quality though the colors can be quite vivid. There are three different types of objective stops that can be used. They are the central stop, the oblique stop, and the annular stop. The first two are the most useful.