Variable Contrast Optical Pattern Generator

摘要

This invention is directed to an optical apparatus by which patterned images may be formed and varied in contrast while maintaining substantially constant photometric luminance. Two beams of spectrally similar luminous energy, one patterned and the other substantially homogeneous, are projected through orthogonal linear polarizers and into a beam combining device. If the pattern is periodic and has a space average transmission equal to half the sum of the maximum and minimum levels, a rotating polarizer in the path of the output beam can alter the contrast of the projected image without varying the average photometric luminance. Such operation presupposes that the two afore-mentioned beams are attenuated to balance their average photometric luminance prior to being combined. The central feature of the invention resides in the intermediate alignments of the rotating polarizer, where both beams are partially transmitted and partially attenuated. As disclosed and claimed in this application the pattern image may be varied in contrast, while average photometric luminance remains constant, by using the embodying apparatus in the manner taught.