Focus error detection device

Details Focus error detection device Focus error detection device

1983-06-16

1986-12-23

Willis, Davis L.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 45, G01J 120

Patent

active

046313966

ABSTRACT:
A focus error detection device for use with a system for optically recording and reading out information, and which can produce a symmetrical focus error signal with respect to the amount of displacement of the reflecting surface of the recording medium from an in-focus position. A second cylindrical lens whose axial direction is perpendicular to the axial direction of a first cylindrical lens is provided, and lateral magnification between the position of the receiving surface of a photo detector and a conjugate plane, which is located adjacent to the in-focus position of the reflecting surface, is made uniform in each direction. By this feature, the output signal of the photo detector varies in a symmetric manner in both directions from the in-focus position of the reflection surface.

REFERENCES:
patent: 4025949 (1977-05-01), Whitman
patent: 4280215 (1981-07-01), Okano

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