Robust method for determining an imaging system focus error

Details Robust method for determining an imaging system focus error Robust method for determining an imaging system focus error

1993-06-10

1995-03-07

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

354407, G01J 120

Patent

active

053960580

ABSTRACT:
A robust method for determining a radiation imaging system focus error, that employs a focus sensor and an accompanying curve determined analytically or empirically according to the characteristics of the sensor, is disclosed. In a preferred embodiment, the focus sensor comprises two beamsplitters, a spacer, and three detectors comprising CCD array. The three detectors are constrained to satisfy radiation path length specifications, with respect to the beamsplitters and spacer. In the method, the curve representing variance vs. focus position is empirically determined. The focus sensor may then be aligned in an unused portion of an imaging system radiation field. The detectors simultaneously image the same scene, sampling it at three different focus positions. These sampled points are then fit to the empirically determined curve; a maximum of the fitted curve is a robust measure of the imaging system focus error.

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patent: 4633075 (1986-12-01), Sakai et al.
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