Mirror focussing system with narrow viewing angle

Abstract

A telescope employs folded optics with multiple reflections between a concave primary reflector, oriented towards incoming radiation, and a convex secondary reflector to produce reflected imaging rays which are nearly parallel to the optic axis of the telescope. Such geometry permits extremely long focal length (high f numbers) systems in a very overall short length, and the insertion of tubular barriers, both of which serve to intercept rays of radiation from a strong source which is sufficiently close, in an annular sense, to the object being viewed to produce a glare which would mask the image. The structure of the telescope includes apertures in both the primary and secondary reflectors situated along the optical axis to permit the reflected rays to pass beyond the secondary reflector to a point in front of the focus of the primary reflector as well as to a point behind the primary reflector, but which block out off-axis rays outside the field of interest. The tubular barriers are positioned at the locations of the apertures so as to further block unwanted rays of radiation. The concave mirror positioned ahead of the focus of the primary reflector directs reflected rays back through the aperture of the secondary reflector towards the aperture in the primary reflector for detection by a sensor of the radiation.