Off-axis three-mirror anastignat having corrector mirror

Claim 1

An all-reflective optical system for receiving and focusing optical signals comprising: (a) a primary mirror having an optical axis and a concave reflecting surface yielding significant net positive optical power and operable to create a subsequent intermediate image; (b) a real unobscured entrance pupil displaced from said optical axis and located prior to said primary mirror; (c) a significant two dimensional field of view displaced from said optical axis that is substantially in focus at said intermediate image; (d) a low power corrector mirror having a general aspheric reflecting surface and positioned between said primary mirror and said intermediate image; (e) a secondary mirror having a convex reflecting surface yielding significant net negative optical power and positioned subsequent to said intermediate image; (f) a tertiary mirror having a concave reflective surface yielding significant net positive optical power and positioned subsequent to said secondary mirror; (g) a final image surface that is substantially flat and located subsequent to said tertiary mirror and is optically conjugate to said intermediate image by the operation of said secondary and tertiary mirrors; and (h) a real unobscured exit pupil displaced from said optical axis and positioned between said tertiary mirror and said final image surface and optically conjugate to said entrance pupil by the operation of said primary, corrector, secondary, and tertiary mirrors.