Abstract

A geometric focus error detection method is introduced in which a pair of photodetectors is placed equidistant from the image of the focus formed by the objective lens when defocus approaches infinity. The focus error signal (FES) has an overall shape of the familiar S-curve and theoretically only one zero crossing exists which occurs at zero defocus.

© 1986 Optical Society of America

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Author Affiliations

Gilbert Y. Chan

The author is with Aerojet ElectroSystems Company, P.O. Box 296, Azusa, California 91702-0296.

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