Ritchey-Chrétien telescope

Ritchey-Chrétien is a type of astronomical telescope. It is a specialized Cassegrain[?] reflector with the advantage that it is coma free. This is why almost every professional reflector telescope in the world is of the Ritchey-Chrétien design. It was invented by George Willis Ritchey and Henri Chrétien in the early 1910's.