Automatic focusing of optical systems

Claim 2

An automatic focusing system for an optical correlator having a transform plane defining an input aperture, an optic system including a movable focusing lens, and an output slit arranged in sequence on an axle, comprising: a beam splitter intersecting the axis between the optic system and the output slit; a mirror receiving the image projected by the beam splitter, the mirror having a pair of reflective surfaces angled relative to one another to produce spacially separated images; target means receiving the images projected from the mirror and producing electrical signals proportional to image relative position; a focusing signal generating means wherein a long delay circuit receives the electrical signals and the output thereof drives a short delay circuit, the difference between the output of the long delay circuit and that of the short delay circuit being created in a difference circuit, the output of the difference circuit being multiplied with the electrical signals in a multiply circuit, result thereof being integrated in an integrator circuit, the output of which is directly related to the direction and magnitude of focusing error; and means for shifting the movable lens along the axis of the optical correlator in response to the output of the integrator circuit.

Claim 3

An automatic focusing system for an optical system having a focusing lens movable along the optical axis of the optical system, comprising: a beam splitter intersecting the optical axis between the focusing lens and the image focal plane; a mirror receiving the beam projected by the beam splitter, the mirror having a pair of reflective surfaces angled relative to one another for separating a beam into spacially separated images, an upper image and a lower image; image detection means receiving and scanning the images projected by the mirror and producing output signals, an upper output signal and a lower output signal, according to the images so received, the upper and lower output signals being separated by the time required for the image detection means to scan between the upper and the lower images, such time being the scan time; a first delay circuit means delaying the output signals an amount of time equivalent to the scan time less one-half a resolvable element, where a resolvable element is the minimum amount of time required for the image detection means to sense an image projected to it and produce a corresponding output signal; a second delay circuit means further delaying the output of the first delay circuit means one-half of a resolvable element; a third circuit means inverting the output of the second delay circuit means and adding to it the output of the first delay circuit means; a fourth circuit means multiplying the output of the image detection means with the output of the third circuit means; a fifth circuit means receiving and integrating the output of the fourth circuit means; and means for moving the lens along the optical axis in response to the magnitude and sign of the output of the fifth circuit means.

Claim 4

An automatic focusing system for an optical system having a focusing lens movable along the optical axis of the optical system, comprising: a beam splitter intersecting the optical axis between the focusing lens and the image focal plane; a mirror receiving the beam projected by the beam splitter, the mirror having a pair of reflective surfaces angled relative to one another for separating a beam into spacially separated images, an upper image and a lower image; image detection means receiving and scanning the images projected by the mirror and producing output signals, an upper output signal and a lower output signal, according to the images so received, the upper and lower output signals being separated by the time required for the image detection means to scan between the upper and the lower images, such time being the scan time; a first delay circuit means delaying the output signals an amount of time equivalent to the scan time less one-half a resolvable element, where a resolvable element is the minimum amount of time required for the image detection means to sense an image projected to it and produce a corresponding output signal; a second delay circuit means further delaying the output of the first delay circuit means one-half of a resolvable element; a third circuit means inverting the output of the second delay circuit means and adding to it the output of the first delay circuit means; a fourth circuit means multiplying the output of the image detection means with the output of the third circuit means; a fifth circuit means receiving and integrating the output of the fourth circuit means; and means for moving the lens along the optical axis in response to the magnitude and sign of the output of the fifth circuit means.

Claim 5

An automatic focusing system according to claim 2 wherein the image detection means comprises a vidicon.

Claim 6

The automatic focusing system according to claim 2 wherein the output, F, of the fifth circuit means is given by the formula where IL (x) and IU (x) are, respectively, the lower and upper output signals of the image detection means, delta is one resolvable element, Xmin equals the minimum x co-ordinate detected by the image detection means, and Xmax equals the maximum x co-ordinate detected by the image detection means.

Claim 7

An automatic focusing system according to claim 2 wherein the mirror is rotatable to track image motion in the optical system and maintain the images projected to the detecting means stationary.

Claim 8

An automatic focusing system according to claim 2 wherein a slit is provided between the beam splitter and the mirror, with the slit being located at the image focal plane of the optical system.

Claim 9

An automatic focusing system according to claim 6 further including a field lens imaging the optical system transform plane on the mirror and a transfer lens system imaging the slit on the detecting means.