a type of reflecting telescope. In this system, the parallel beams of light from stars strike a primary concave hyperbolic mirror, are reflected to a secondary convex hyperbolic mirror, and are focused below the secondary mirror forming the image. Spherical aberrations and coma are corrected in a Ritchey-Chrétien reflector system, and the field of view may reach 0.5–1°. Special corrector lenses are used to correct astigmatism and increase the field of view to 2°.
The system was proposed by the French optician H. Chrétien in 1922 and first constructed by the American astronomer G. Ritchey in 1928. It came into wide use in the second half of the 20th century.