Korsch telescope

A Korsch telescope is a type of three-mirror-anastigmat reflector telescope which was described in 1972, the design including a concave ellipsoidal primary, a convex hyperbolic secondary, and a concave ellipsoidal tertiary mirror. It does well reducing common aberrations, its focal plane is flat and can be made to avoid stray light. Examples:

• James Webb Space Telescope (JWST).
• Euclid.
• THESEUS IRT (concept).

The Rubin Observatory telescope uses a two-mirror variant of the design termed an Eisenberg-Pearson telescope, in which a portion of the first mirror functions as the third.