Precision ellipsoidal mirrors have use in telescopes
Ellipsoidal mirrors are produced of Zerodur, BK7, and fused silica, with typical surface accuracy of >λ/10 (dependent on size and radius) and surface quality of 20:10 scratch-dig. Custom and prototype ellipsoids are offered in various shapes up to a dimension of 650 mm. They are used in telescopes, beam expanders/reducers, and grazing incidence imaging.
Optical Surfaces
Kenley, U.K.