Lens focus shift sensor

Details Lens focus shift sensor Lens focus shift sensor

1996-04-03

1999-11-23

Moses, R. L.

Photocopying

Projection printing and copying cameras

Step and repeat

355 67, 356399, 356400, 356401, 356374, G03B 2742, G03B 2754, G01B 1114

Patent

active

059910046

ABSTRACT:
A focus shift sensor includes a light source which directs light through a first grating to form a pattern of light. The pattern is directed through the lens which images the pattern at a second grating. The two gratings have different periods such that the second grating generates a pattern of Moire fringes which are projected onto a CCD array. The second grating is preferably tilted with respect to the plane of the image of the pattern from the first grating such that only a portion of the second grating is within the range of focus of the lens. As a result, a pattern of shortened Moire fringes is produced. As the range of focus shifts along the second grating, the Moire fringes move along the CCD array. The movement of the fringes is tracked and the system is adjusted to maintain the location of the focal plane of the lens at a desired location.

REFERENCES:
patent: 4549084 (1985-10-01), Markle
patent: 5189494 (1993-02-01), Muraki
Gregoris, Dennis, and Ristic, Velimir M., "Moire interferometric focusing system for optical microlithography," Applied Optics, 2 20 (Oct. 15, 1987) .

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