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 manufacturing the specified mirrors is too much of a challenge. The optical analysis Schwarzschild developed leading up to this design has been used by others, developing some of the widely-used 20th-century telescope types. One subsequent variant of Schwarzschild's design is the Couder telescope (aka Schwarzschild-Couder telescope).