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Abstract

The invention relates to a high performance optical system for a wide angle IR imager requiring a cryogenic environment for the IR detector array. The wide angle requirement makes it necessary for one lens to be behind a 'cold aperture' within the cryogenic environment where focusing is difficult and performance of the aperture reduced. These objectives are minimized by use of a telecentric lens pair, one member of which is within the cryogenic environment. The telecentric lens pair refocuses the primary image formed by an objective lens, permitting a high quality image to be formed on the IR detector array. The usual errors in positioning the internal lens, which might impair the quality of the focused image, are avoided by a compensatory repositioning of the externally accessible objective lens. The use of collimated bundles of light, characteristic of telecentric lens pairs, permits maximum aperture efficiency, and also provides a fourier transformation plane in which spatial filtering may be used to reduce IR background of low spatial frequency.

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First Claim