Method for determining an imaging system focus error

Claim 1

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, the sensor including elements comprising: a) a first beamsplitter comprising an input scene radiation surface, and a first and second output surface; b) a second beamsplitter located to be in a radiation path generated by the first output surface of the first beamsplitter, and comprising an input radiation surface, and a first and a second output surface; c) a first radiation detector located to be in a radiation path generated by the first output surface of the second beamsplitter, and defining a first imaging surface located at a known radiation path length D 1 as measured from the input surface of the first beamsplitter; d) a second radiation detector located to be in a radiation path generated by the second output surface of the second beamsplitter, and defining a second imaging surface located at a known radiation path length D 2 , as measured from the input surface of the first beamsplitter; and e) a third radiation detector located to be in a radiation path generated by the second output surface of the first beamsplitter, defining a third imaging surface located at a known radiation path length D 3 , as measured from the input surface of the first beamsplitter; the elements so constrained that: D.sub.1 ≠ D.sub.2 ≠ D.sub.3 ≠ D.sub.1 ; 2) 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; 3) 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 4) determining, from the recorded data, a value of a parameter representative of a statistical distribution of intensity vs. surface point position of the sampled field for each of the three imaging surfaces; b) generating a parabolic function of value of the parameter vs. imaging surface location by curve fitting to three points specified by the three imaging surface locations and the respective parameter values derived for the three imaging surfaces from step 4a; c) computing a location of an optimal imaging surface, corresponding to a maximum value of the parameter for the parabolic function, the computed optimal imaging surface location serving as a measure of the magnitude and direction of the imaging system focus error.

Claim 2

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, the sensor including elements comprising: a) a first beamsplitter comprising an input scene radiation surface, and a first and second output surface; b) a second beamsplitter located to be in a radiation path generated by the first output surface of the first beamsplitter, and comprising an input radiation surface, and a first and a second output surface; c) a first radiation detector located to be in a radiation path generated by the first output surface of the second beamsplitter, and defining a first imaging surface located at a known radiation path length D 1 as measured from the input surface of the first beamsplitter; d) a second radiation detector located to be in a radiation path generated by the second output surface of the second beamsplitter, and defining a second imaging surface located at a known radiation path length D 2 , as measured from the input surface of the first beamsplitter; and e) a third radiation detector located to be in a radiation path generated by the second output surface of the first beamsplitter, defining a third imaging surface located at a known radiation path length D 3 , as measured from the input surface of the first beamsplitter; the elements so constrained that: D.sub.1 ≠ D.sub.2 ≠ D.sub.3 ≠ D.sub.1 ; 2) 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; 3) 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 4) determining, from the recorded data, a value of a parameter representative of a statistical distribution of intensity vs. surface point position of the sampled field for each of the three imaging surfaces; b) generating a parabolic function of value of the parameter vs. imaging surface location by curve fitting to three points specified by the three imaging surface locations and the respective parameter values derived for the three imaging surfaces from step 4a; c) computing a location of an optimal imaging surface, corresponding to a maximum value of the parameter for the parabolic function, the computed optimal imaging surface location serving as a measure of the magnitude and direction of the imaging system focus error.

Claim 6

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 ε short of the ideal focus point, and a distance epsilon ε 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; deriving a parabolic function of variance versus image plane location which fits the points defined by the values of statistical variance computed for each of the first, second and third image plane locations; and from the derived parabolic function, determining the distance and direction, from the first image plane location, of the image plane location that corresponds to the point of maximum variance on the parabolic function 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.

Claim 7

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 ε short of the ideal focus point, and a distance epsilon ε 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; deriving a parabolic function of variance versus image plane location which fits the points defined by the values of statistical variance computed for each of the first, second and third image plane locations; and from the derived parabolic function, determining the distance and direction, from the first image plane location, of the image plane location that corresponds to the point of maximum variance on the parabolic function 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.

Claim 15

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 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 different first, second and third known distances from the reference point of the system; 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; deriving a parabolic function of variance versus image plane location which fits the points defined by the values of statistical variance computed for each of the first, second and third image plane locations; and from the derived parabolic function, determining the distance and direction, from the reference point location, of the image plane location that corresponds to the point of maximum deviation on the parabolic function 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.

Claim 16

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 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 different first, second and third known distances from the reference point of the system; 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; deriving a parabolic function of variance versus image plane location which fits the points defined by the values of statistical variance computed for each of the first, second and third image plane locations; and from the derived parabolic function, determining the distance and direction, from the reference point location, of the image plane location that corresponds to the point of maximum deviation on the parabolic function 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.