Optical system for wide angle IR imager

In an IR sensor head containing an IR detector array installed within a cryogenic enclosure, said sensor head exhibiting a wide field of view, high optical performance and high cold shielding efficiency, the combination comprising:

• (A) a first objective lens having a focal length (f1) installed on said optical axis for imaging the object field into a primary image plane,
• (B) an evacuated cryogenic, cold shielding enclosure, including
• (1) an aperture in the cold shield installed on said optical axis for admission of IR image radiation and for stopping unfocused IR background illumination, and
• (2) cooling means
• (C) an IR detector array installed in said enclosure on said optical axis and cooled by said cooling means, and
• (D) a telecentric lens arrangement comprising
• (1) a second lens having a focal length (f2) installed outside said enclosure on said optical axis at a distance from said primary image plane for collimating the ray bundles of said primary image points,
• (2) a third lens having a focal length (f3) installed within said enclosure on said optical axis at a distance from said IR detector array for focusing said collimated ray bundles of said image points into a secondary image plane on said IR detector array,
• said cold shield aperture being spaced between said second and third lenses, and of minimum size for intercepting said collimated ray bundles for maximum aperture efficiency,
• said arrangement permitting correction of inaccuracy in the positioning of said third lens in relation to said IR detector array by a compensatory repositioning of said objective lens in relation to said telecentric lens arrangement without a significant loss in optical performance.