A type of three-mirror reflecting telescope that produces a wide field of view without spherical aberration, coma, astigmatism, or curvature of field. The design was first published in 1972 by the American optician Dietrich G. Korsch (1937–94). As in a Cassegrain reflector, a Korsch telescope has a concave primary mirror and a convex secondary, but with the addition of a concave third mirror (the tertiary). After passing through a central hole in the primary, the light beam either falls directly onto the tertiary or is folded to one side off a plane mirror for compactness. The James Webb Space Telescope is of Korsch design.