Patent ID: 6118578
Filing Date: 2000-09-12
Classification: G02B

Abstract:
An infrared (IR) afocal lens assembly for providing an observed magnified IR image scene with alternative field of view and a substantially lens temperature independent performance, the IR afocal lens assembly comprising:a collecting lens on an optical axis for collecting IR input light, said collecting lens further including a GaAs meniscus lens;a focusing lens subassembly on the optical axis after said collecting lens for providing focus, said focusing lens subassembly including one focusing single GaAs lens and one focusing single ZnS lens, said focusing lens subassembly movable along the optical axis to provide range focus;an intermediate focal plane on the optical axis after said focusing lens subassembly, said intermediate focal plane having an intermediate focus;an eyepiece lens subassembly on the optical axis after said intermediate focal plane for collimating the intermediate focus and providing an external exit pupil, said eyepiece lens subassembly including one eyepiece single ZnS lens and one eyepiece single GaAs lens,an aperture stop on the optical axis which defines the exit pupil of the IR afocal assembly, whereby substantially no change in index of refraction and absorption occurs with increase in lens temperatures up to approximately 100 degrees Celsius, and such that a narrow field of view (NFOV) of an IR image is observed magnified through the IR afocal lens assembly.