IR radiation detector for target sighting - has cassegrain optical system which retro-reflects incoming light into hollow conical reflector with end detector

摘要

The infra-red beam target finder uses a CAssegrain type optical system (34). Incoming light passes through a transparent coupler (32) to a reflector mirror (38) with a central aperture containing a conical holder (46), the narrow end of which has a circular ring which supports a flat plate window (44) retained in a smaller cone (42) with a centrally situated plane mirror (40). - The plane mirror retro-reflects the incoming light to a small aperture containing a field lens (63), which is opposite and coaxial with a modulator disc (64) at the end of a vacuum tube (48). The incoming light beam continues to a beam pupil lens (62) at the end of a narrowing conical tube (66) which by continuous internal reflection concentrates the beam onto a detector element (58) at the end of a vacuum tube.