Based on measuring the contrast of moire fringes produced by digital subtraction, an alternative method for object positioning is presented. We use a model of fringe visibility mismatch due to defocusing and search for a global maximum as the best focusing criterion. Both laser and white light illumination are tested. Experimental results shows an accuracy of 0.5 mm.
Roberto Daniel Torroba,
L. C. S. Nunes,
Alberto A. Tagliaferri,
"Object positioning by a digital moire focusing technique," Optical Engineering 38(8), (1 August 1999). http://dx.doi.org/10.1117/1.602191