An optical design for a reflecting telescope that has an exceptionally wide field of view with good definition. It uses a paraboloid primary of focal ratio f/4 or less, a convex spherical secondary mirror, and a concave spherical third mirror with curvature equal but opposite to that of the secondary. It was devised by the French optician Maurice Paul in 1935 and discovered independently by James Baker in about 1945. See also: Willstrop telescope.