Catadioptric telescopes use a combination of two systems. They form an image with the use of a mirror (catoptric system) and lens (dioptric system).
The main elements of catadioptric telescopes are:
The path of light in Catadioptric telescope (Available from https://sites.google.com/site/mrwilkinsonphysics/classes/s4-physics/optical-telescopes. [accessed 29 Oct 2019] )
The optical tube is sealed and quite small in size. The light enters the optical tube and passes through the glass corrector, installed at the front of the optical tube. The primary function of the glass corrector is to limit the spherical aberration. Light rays travel to the primary mirror at the bottom of the telescope. The beams are collected and bounced towards the secondary mirror. From here, the light reflects through a hole in the primary mirror to an eyepiece.
With the right position of mirrors and lens, the light is "optically folded," meaning that the effective focal length of the telescope increases while the mass reduces – which makes telescopes easier to produce.
The most popular designs are:
Both telescopes are very popular and have a pretty similar design, but there are some differences. The main difference is in their corrector plate and secondary mirror.
Maksutov-Cassegrain uses a thicker corrector lens and a different secondary mirror that is located inside of the corrector lens. Telescopes also have different aperture sizes – Schmidt-Cassegrain is designed to have a bigger aperture than Maksutov-Cassegrain.
Catadioptric teleskopes have shorter optical tube than refractors and reflectors. This means that they take up less space and are easier to move. Their secondary mirror degrades the performance for planetary and Moon observations, but overall they are still great for observing all celestial objects.