Newtonian-Cassegrain telescope

A Newtonian-Cassegrain telescope is a Cassegrain telescope fitted with a flat diagonal mirror to intercept the converging beam from the secondary and reflect it to the side of the tube. Unlike a standard Cassegrain, the primary mirror does not need a central hole, and the focal position can be arranged to coincide with the declination axis of the mounting to give a stationary observing position.