Depth of field in the scanning microscope

Abstract

Various definitions of depth of field in the microscope are discussed. The variation in the integrated intensity in the image of a point object outside the focal plane shows how the microscope discriminates against such objects. The power diffusely scattered by a translucent object is also considered. A Type-2 scanning microscope is found to have a much reduced depth of field according to these criteria, which makes it useful for studying thick biological slices. These results do not contradict the claim that depth of field may be much increased in such a microscope by using lenses with annular pupil functions.