1. An optical system comprising:
a catadioptric subsystem configured to collect light from an object;
a refractive subsystem configured to form an image of the object through the catadioptric subsystem; and
a baffle arranged along an optical axis of the optical system and configured to block light, which travels toward the refractive
subsystem without being reflected by the catadioptric subsystem, to form a shielded portion in a center of an exit pupil plane
of the optical system,
wherein the catadioptric subsystem includes a partially transparent surface around the optical axis so that transmissivity
of a region, other than the shielded portion, in the exit pupil plane varies in a radial direction of the exit pupil plane.