Optical system for a wide field of view staring infrared sensor having improved optical symmetry

A method for operating a wide-angle infrared radiation (IR) imaging system having an entrance aperture for admitting IR from a scene, said IR imaging system having a dewar that contains a coldshield that encloses a cooled IR detector array disposed at an image plane, said dewar comprising a dewar window, where an optical axis of said IR imaging system passes through said dewar window to said image plane, the method comprising:

• providing along said optical axis between said entrance aperture and said dewar window a plurality of uncooled optical elements and a plurality of reflector segments, each of said reflector segments having a generally annular reflective surface facing said dewar window, said reflective surface surrounding an IR transmission path region through said reflector segment;
• defining an effective cooled aperture stop of said IR imaging system as being coincident with said IR transmission path region through a reflector segment that is furthest from said dewar window;
• and
• locating at least one of said optical elements between said effective cooled aperture stop and another one of said reflector segments that is located nearer to said dewar window.

A wide-angle infrared radiation (IR) imaging system having an entrance aperture for admitting IR from a scene and an image plane upon which the scene is imaged, comprising:

• a dewar that encloses a cooled IR detector disposed at the image plane, said dewar comprising an outer window, a coldshield, and said detector;
• a multi-element lens that comprises a plurality of uncooled optical elements disposed along the optical axis between said entrance aperture and said dewar window;
• an optical stop disposed within said uncooled optical elements such that lens optical power is distributed on both sides of the optical stop;
• and
• at least one reflector element comprising at least one inner opening and at least one surface having a generally toroidal surface shape, and having one of the at least one inner openings placed substantially coincident with said optical stop.