Optical processing was first used as an integral part of a holographic microscope by McFee. (Ref. 1) Studying crystal growth from the melt, he inserted a field lens in the recording and reconstruction system. Upon reconstruction he could insert a spot diaphragm at the focal point of the lens to accomplish dark field illumination. He could also insert a phase plate at the same location to accomplish phase contrast. These techniques primarily enhance edge contrast in the reconstructed image.