A Ritchey-Chrétien is a Cassegrain telescope with two hyperbolic mirrors, which removes coma and gives a flat, sharp field well suited to deep-sky imaging of galaxies and small nebulae. The iOptron RC6, RC8 and RC10 cover 6 to 10 inches of aperture, and the Photron RC10 truss tube offers the 10-inch in a lighter open-truss design. Most imagers add a field flattener for larger sensors; see Flatteners, Reducers & Correctors.
