US 5,862,265 A · Separation apparatus and method for measuring focal plane

Abstract

A computer receives image data from a star-shaped optical target in the object plane and calculates angle-dependent boundary sharpness. The horizontal, x-direction, amplitude derivative and the vertical, y-direction, amplitude derivative are computed over a portion of each star pattern image from a Z panning sequence. A microscope slide stage, carrying the target, is moved vertically from a level just below where the target is in focus to a level just above where the target is in focus. For each small increment of vertical motion, Z panning, an image of the star pattern is captured for analysis. Computations are performed on the differentiated images to search for evidence of elongation of the point spread function and variation with stage Z position of the angle of long axis of such an out-of-round point spread function. The presence of a distorted point spread function that varies along the optical axis indicates astigmatism.

Claims26

Dependent claims

An apparatus for evaluating a condition of an optical system comprising:

(a) means for acquiring a plurality of images of a test pattern at different focus positions, having a plurality of images output;
(b) means, connected to the plurality of images output, for processing the plurality of images to compute a plurality of center of gravity vectors, one center of gravity vector for each one of the plurality of images, having a plurality of center of gravity vectors output;
(c) means, connected to the plurality of center of gravity vectors output, for computing a focal plane separation from the plurality of center of gravity vectors, having a focal plane separation output;
and
(d) means, connected to the focal plane separation output, for relating the condition of the optical system to the focal plane separation, having a condition of the optical system output.

2 more elements

An apparatus for qualifying an optical system for compliance with a standard for low astigmatism, comprising:

(a) means for finding a best focus position for an image of a test pattern, having a best focus position output;
(b) means, connected to the best focus position output, for centering the test pattern, having a centered test pattern output;
(c) means, connected to the centered test pattern output, for acquiring a set of images of the test pattern;
(d) means, connected to receive the set of images, for determining vertical motion limits for a Z panning sequence through a Z panning range by obtaining a series of images of the test pattern and examining the series of images of the test pattern for overall resolution, having a resolution examined output;
(e) means, connected to the resolution examined output, for determining a vertical position yielding a best overall resolution for a middle of the Z panning range;
(f) means for acquiring the set of images, beginning at a lower limit of a stage elevation, passing through a plane of best focus, and extending to an upper limit of the stage elevation;
(g) means, connected to receive the set of images, for filtering the set of images to generate a set of filtered test pattern images;
(h) means, connected to receive the set of filtered test pattern images, for computing an estimate of a sharpness of each of a set of boundaries disposed at various angles, having an angle resolution output;
(i) means, connected to the angle resolution output, for finding an angle of highest resolution for each image in a z-panning sequence, having a highest resolution output;
(j) means, connected to receive the set of images, for computing an estimate of a severity of eccentricity of a point spread function for each image in a Z panning sequence;
(k) means, connected to receive the set of images, for finding a first and second dominant angle displaced above and below a plane of least confusion, having a dominant angle output;
(l) means, connected to receive the dominant angle output, for measuring a focal plane separation based on a Z dependent resolution for boundaries at the first and second dominant angles, having a focal plane separation output;
and
(m) means, connected to the focal plane separation output, for applying test criteria to the focal plane separation output.

11 more elements

Dependencies are inferred from the claim text.

Separation apparatus and method for measuring focal plane

Life of this patent

Separation apparatus and method for measuring focal plane

Life of this patent

Abstract

Claims26