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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Vol. 36, Iss. 28 — Oct. 1, 1997
  • pp: 7204–7209

Digital method for measuring the focus error

Adolf W. Lohmann, David Mendlovic, and Zeev Zalevsky  »View Author Affiliations


Applied Optics, Vol. 36, Issue 28, pp. 7204-7209 (1997)
http://dx.doi.org/10.1364/AO.36.007204


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Abstract

We show how the focus longitudinal error z can be deduced from the observed image. This deduction requires some digital image processing. Once the focus error z is known, one may compensate for it either by shifting the lens or by deblurring the image digitally. We have studied systems with a circular or with a rectangular aperture. In the former case, the defocus causes some dark rings in the frequency spectrum of the image. With a rectangular aperture, the defocus creates a set of straight, orthogonal dark lines. These dark zones provide a quantitative diagnosis of the focus error. Some experimental evidence supports our concept.

© 1997 Optical Society of America

History
Original Manuscript: February 6, 1997
Revised Manuscript: March 28, 1997
Published: October 1, 1997

Citation
Adolf W. Lohmann, David Mendlovic, and Zeev Zalevsky, "Digital method for measuring the focus error," Appl. Opt. 36, 7204-7209 (1997)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-36-28-7204

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