Cassegrain telescope
(ˈkæsɪˌɡreɪn) n (Astronomy) an astronomical reflecting telescope in which incident light is reflected from a large concave paraboloid mirror onto a smaller convex hyperboloid mirror and then back through a hole in the concave mirror to form the image
[C19: named after N. Cassegrain, 17th-century French scientist who invented it]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014