This paper describes and gives some of the results of using a microscope which increases the useful depth of observation of an object in a photograph to many times the focal depth of the lens system being used. The principle of the microscope is that the object is illuminated only on the focal plane while the object is being scanned through that plane. Thus, the out-of-focus parts of the object are always in darkness, and the final photographs show high resolution throughout the depth of scan. The mechanism of scanning is somewhat similar to the Gregory–Donaldson method, whereas the mechanism of illumination is similar to that of the Schmaltz slit. This is the first time that scanning and focal plane illumination have been combined to attain high resolution at great depths. Of course, high-frequency scanning would permit direct observation by eye.
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