Cassegrain telescope

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Cassegrain telescope

A compound reflecting telescope designed, according to some sources, by a French sculptor, Sieur Guillaume Cassegrain, in 1672. Others attribute its invention to a 17th-century astronomer known to us only as N. Cassegrain. It is similar to the Gregorian telescope but has a secondary mirror with a convex hyperboloid shape mounted inside the focal plane of the primary mirror. The telescope has a small field, limited mainly by coma, but is compact, portable, and easily mounted and thus very popular. Most large modern reflectors include this facility. See Cassegrain configuration; catadioptric telescope; Ritchey–Chrétien optics; Schmidt telescope.

Cassegrain telescope

[kas·gran ′tel·ə′skōp]
(optics)
A reflecting telescope in which a small hyperboloidal mirror reflects the convergent beam from the paraboloidal primary mirror through a hole in the primary mirror to an eyepiece in back of the primary mirror.