Cassegrain telescope

Type of reflecting telescope in which light collected by a concave primary mirror is reflected onto a convex secondary mirror, which in turn directs it back through a hole in the primary mirror to a focus behind it. As a result, the telescope tube can be kept short, allowing equipment for analysing and recording starlight to be mounted behind the main mirror. All modern large astronomical telescopes are of the Cassegrain type.

It is named after the 17th-century French astronomer Cassegrain who first devised it as an improvement to the simpler Newtonian telescope.