Schwarzschild telescope

A Schwarzschild telescope is a two-mirror reflector telescope with two specific shapes of concave aspheric mirror (meaning not spherical, but the term is generally used when no more-specific term, such as parabolic mirror or hyperbolic mirror, is commonly used). The design produces a flat focal plane, eliminates or limits a number of aberrations, and supports a short focal length suitable for a large field of view. Karl Schwarzschild developed the design in the early 1900s, but it has never been (commonly) used because of the challenge of manufacturing the specified mirrors. The optical analysis Schwarzschild developed that led to this design has been used by others, developing some of the widely-used 20th-century telescope types. One subsequent variant of Schwarzschild's specific design is the Couder telescope (aka Schwarzschild-Couder telescope).