US 5,396,058 A · Robust method for determining an imaging system focus error

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.

Claims24

Dependent claims

A method for quantitatively determining an imaging system focus error, the imaging system inputting a scene radiation field and re-imaging it at an ideal focal point, the method comprising the steps of:

1) providing a sensor having a first, second, and third radiation detector;
2) calibrating said sensor in order to generate a reference curve which accurately represents a functionality of said sensor;
3) positioning the sensor in a portion of the input scene radiation field, and orienting the sensor so that the three radiation detectors each simultaneously image the same scene radiation field, for sampling it at the three different imaging surfaces;
4) sampling the input scene radiation field at the first, second and third imaging surfaces, for recording, respectively, data corresponding to the radiation intensity of the sampled field at different points on each of the three imaging surfaces;
and
5) computing an optimal imaging surface location which serves as a measure of the imaging system focus error.

3 more elements

A method for real time, automatic quantitative determination of distance and direction of displacement along an optical axis of the position of an in-focus image of an input scene radiation field focused by a radiation imaging system, from the position of a predetermined ideal focus point of the system, the method comprising the steps of:

dividing the input scene radiation field into first, second and third scene radiation field paths using beamsplitters;
simultaneously sampling the input scene radiation field along the first, second and third paths, using first, second and third radiation detectors defining first, second and third imaging planes respectively located at the ideal focus point, a distance epsilon .epsilon. short of the ideal focus point, and a distance epsilon .epsilon. beyond the ideal focus point;
computing a value of statistical variance based on intensity of the input scene radiation field sampled at different points in the imaging plane for each of the first, second and third imaging planes;
calibrating said sensor in order to generate a reference curve which accurately represents a functionality of said sensor;
and
from the generated reference curve, determining the distance and direction, from the first image plane location, of the image plane location that corresponds to the point of maximum variance of said reference curve;
the determined distance and direction representing the distance and direction of displacement of the position of the in-focus image from the position of the ideal focus point.

4 more elements

A method for real time, automatic quantitative determination of distance and direction of displacement along an optical axis of the position of an in-focus image of an input scene radiation field focused by a radiation point of the system, the method comprising the steps of:

dividing the input scene radiation field into first, second and thirds scene radiation field paths using beamsplitters;
simultaneously sampling the input scene radiation field along the first, second and third paths, using first, second and third radiation detectors defining first, second and third imaging planes respectively located at different first, second and third known distances from the reference point of the system;
computing a value of statistical variance based on the intensity of the input scene radiation field sampled at different points in the imaging plane for each of the first, second and third imaging planes;
calibrating said sensor in order to generate a reference curve which accurately represents a functionality of said sensor;
and
from said generated reference curve, determining the distance and direction, from the reference point location, of the image plane location that corresponds to the point of maximum deviation of said reference curve;
the determined distance and direction representing the distance and direction of displacement of the position of the in-focus image from the position of the reference point.

4 more elements

Dependencies are inferred from the claim text.

Robust method for determining an imaging system focus error

Life of this patent

Robust method for determining an imaging system focus error

Life of this patent

Abstract

Claims24