Nasmyth Reflector System

a variant of the Cassegrain reflector system in which an additional plane mirror is placed in the beam of rays that are converging at the focus. The mirror reflects the rays to the wall of the telescope tube, where a light-detecting device is located. This type of reflector was proposed by J. Nasmyth in the mid-19th century. It is used in the 2.6-m reflector at the Crimean Astrophysical Observatory and in a number of other large telescopes.