Catadioptric Telescopes

Sub Categories

Maksutov Cassegrain Telescopes

Schmidt Cassegrain Telescopes

General properties of Catadioptric telescope

The Catadioptric telescope uses a combination of two systems. The Catadioptric telescope forms an image with the use of a mirror (catoptric system) and lens (dioptric system).

The main systems of the telescope are:

a short optical tube,
a primary mirror,
a secondary mirror and
a glass corrector.

Catadioptric telescopes

The path of light in Catadioptric telescopes (Available from https://sites.google.com/site/mrwilkinsonphysics/classes/s4-physics/optical-telescopes. [accessed 29 Oct 2019] )

Path of the light in the optical tube

The optical tube in the Catadioptric telescope 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 of the catadioptric telescope.

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 catadioptric 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 catadioptric - telescopes easier to produce.

The most popular designs of Catadioptric telescopes

Two of the most popular designs of Catadioptric telescope are:

Schmidt-Cassegrain telescope
Maksutov-Cassegrain telescope

Both catadioptric telescopes are very popular and have a pretty similar design, but there are some differences.

The main differences in optical tube assembly

Schmidt-Cassegrain telescope and Maksutov-Cassegrain differ in:

corrector plate and
secondary mirror

Maksutov-Cassegrain telescope uses a thicker corrector lens and a different secondary mirror that is located inside of the corrector lens. Telescopes also have different aperture sizes – The schmidt-Cassegrain telescope is designed to have a bigger aperture than Maksutov-Cassegrain telescope.

Cassegrain Telescopes compare to Refractors and Reflectors

Catadioptric telescopes have shorter optical tubes than refractor telescopes and reflector telescopes. 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 telescopes for observing all celestial objects.

A short presentation of the Catadioptric telescope is available here.