Schmidt camera

A Schmidt camera (or Schmidt telescope) is a reflector telescope with a spherical primary mirror and a particular kind of lens that reduces spherical aberration (called the Schmidt corrector plate). For a given size, a spherical mirror is easier to grind than a non-spherical mirror and produces little of the other aberrations usually associated with a short focal length, allowing Schmidt cameras to be made with a wide field of view (FOV), which is especially suitable for surveys. However, the focal plane is not planar, but curved, thus requiring unique design of the image recording mechanism, such as curved photographic paper, back when photography was used in such research telescopes. The general design of the Schmidt camera was developed by Bernhard Schmidt in 1930, and for two decades, observatories deployed a number of them around the world for sky surveys, the largest with a 2-meter aperture. Newer designs offer similar capabilities, but Schmidt cameras are still built, e.g., for special-purpose space telescopes that need to be compact with a large FOV. Example Schmidt cameras/telescopes:

• Palomar 48 Inch Telescope.
• CTIO Schmidt Camera.
• ESO Schmidt Telescope.
• UK Schmidt Telescope.
• LAMOST.
• Kepler Telescope.
• ULTRASAT.

Variants of the Schmidt camera combine it with other telescope designs, e.g., the Schmidt-Newton telescope (SNT) or Schmidt-Cassegrain telescope (SCT).