Catoptric optical system including concave and convex reflectors

Abstract

This is a catoptric optical system including afocal and focal embodiments comprising substantially aspheric concave first, convex second, third, and concave fourth reflection means producing an intermediate image between the first and fourth reflection means. In an afocal embodiment, the third reflection means is proximate the internal image produced by the second reflection means and provides aberration control and a compact beam folding function. In an alternate focal embodiment, the second reflection means is proximate the internal image produced by the first reflection means. Significant magnifying power is achieved for the afocal embodiment while minimizing aberration and distortion and providing full spectrum coverage with high image quality. The system provides a wide circular or square field of view with little or no obscuration in a compact envelope. The exiting beam is substantially normal to the incident beam and the exit pupil is external, even when the aperture stop is external to, or at, the primary mirror.