Ritchey-Chrétien telescope

A Ritchey-Chrétien telescope (RCT or RC) is a type of reflector telescope that has a specific reflector configuration of two hyperbolic mirrors, designed to limit telescope-induced aberrations. The primary mirror is hyperbolic but very close to parabolic. The secondary mirror is convex and hyperbolic. (This combination of concave primary and convex secondary is termed a Cassegrain telescope, and an RCT may be considered a variant.) The curvature is chosen to eliminate third-order coma (the cubed term of a series-expansion that describes the aberration). The design is common for large research telescopes, including:

• Large Altazimuth Telescope (BTA-6)
• du Pont Telescope.
• Gemini Observatory
• Gran Telescopio Canarias (GTC)
• Keck Observatory
• European Southern Observatory Very Large Telescope (ESO VLT)
• New Technology Telescope (NTT)
• VISTA
• Hubble Space Telescope (HST)
• Pan-STARRS telescopes.
• Sloan Digital Sky Survey (SDSS) telescope
• Spitzer Space Telescope (SST)
• Subaru Telescope
• William Herschel Telescope (WHT)

The design is also common for small telescopes, such as those used in amateur astronomy.