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Abstract

A dual focus objective lens and opposite linear polarizers associated therewith for providing a linearly polarized image at a first focal image plane and an opposite linearly polarized image at a second focal plane. A detector array is positioned at the first focal image plane which is closest to the objective lens. Each pixel site of the detector array has two halves with opposite polarities in each half wherein each half looks at opposite planes of polarization in the two image planes. One plane of polarization receives a focused linearly polarized image of the high spatial frequency target and low spatial frequency background and the other plane of polarization receives a slightly defocused image which contains a defocused image of the high spatial frequency target but a rather faithful reproduction of the low spatial frequency background. The two outputs from each half of the pixel sites are algebraically subtracted by processing electronics leaving a high contrast target image.

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First Claim