CATOPTRIC SYSTEM

PROBLEM TO BE SOLVED: To improve the working reliability of a convex mirror and to reduce cost required for inspection and working by making the convex mirror of an off-axis catoptric system having no center shield to be spherical. SOLUTION: This catoptric system 10 is provided with the 1st concave mirror 11 of aspherical shape, the convex mirror 12 of spherical shape and the 2nd concave mirror 13 of the aspherical shape, and a diaphragm 14 is disposed around the mirror 12. The center of curvature of each reflection mirror is on the optical axis 15 of the system 10, and the system 10 constitutes a coaxial system. Luminous flux 16 from a distant object including a main light beam 17 is made incident on a virtual entrance pupil behind the mirror 11 with a specified angle inclined from the optical axis 15, reflected on the mirrors 11, 12 and 13 in this order and formed a good image on an image surface 18 outside the optical axis 15. As for positional relation between the mirrors 12 and 13, the mirror 12 is arranged substantially at a position to be a half of the radius of curvature of the center of the mirror 13, so that the system 10 substantially constitutes a telecentric optical system.