Catadioptric Telescopes: The Best of Both Worlds

Many beginner-friendly telescopes use either mirrors or lenses to produce the image you see in the telescope. Reflectors, for example, use mirrors, while refractors use lenses. Catadioptric telescopes, though, use both, making them more error-corrective and ideal for experts and scientists.

Catadioptric Optical System

As stated above, a catadioptric optical system uses both refraction and reflection to create a combined optical system. In most cases, this combined system is made via lenses and curved mirrors. In fact, the name “catadioptric” references both parts of this system. “Dioptric” refers to the study of refraction via lenses, while “catoptrics” refers to the study of reflection via mirrors.

This catadioptric optical system can be seen in many places. Searchlights, headlamps, and early lighthouses all use this system. More so, many telescopes and microscopes use catadioptric optical systems.

Why Catadioptric Telescopes are Superior

Catadioptric telescopes are a type of optical telescope that are known for their precision and clarity. The reason for this is that the mirrors and lenses are used to both create the image and correct any errors that may be produced from the reflection or refraction.

In fact, catadioptric telescopes have a greater overall degree of error correction than either reflectors or refractors. They can even have a wider field of view that is essentially aberration-free. Telescopes without aberrations tend to have full-aperture correctors.

Full-aperture correctors are lenses that are placed in front of a spherical primary mirror. They combine the spherical mirror’s reflection ability with a large lens at the front of the tube. This combination allows the spherical mirror to image objects at infinity.

Catadioptric Designs

There are several catadioptric designs. Here are the four most popular:

  • Schmidt-Cassegrain: This telescope consists of a short tube, spherical primary mirror, full-aperture corrector lens, and a convex secondary mirror. The image is formed behind the primary mirror while the secondary mirror reflects light. The image location is why this telescope is classified as a Cassegrain telescope.
  • Maksutov-Cassegrain: The Maksutov-Cassegrain features a short tube, spherical concave primary mirror, full-aperture corrector lens, and convex secondary mirror. The corrector lens is made from a weak negative meniscus lens. The image is formed behind the primary mirror.
  • Schmidt-Astrograph: this telescope is made of mirrors and accessory lenses. Unlike the previous two telescopes, this scope often lacks a full-aperture corrector lens, though you can purchase a modified Schmidt-Astrograph.
  • Schmidt-Newtonian: This telescope is a cross between a Newtonian telescope and a Schmidt-Cassegrain. This telescope differs from the Schmidt-Cassegrain in that the image is formed on the side of the tube.

Downsides of Catadioptric Telescopes

Obviously, catadioptric telescopes are great for their clarity and error-corrective qualities, but there are several reasons why you would opt for another telescope.

Most notably, catadioptric telescopes are much more expensive than regular refractors or reflectors. The reason for this is that catadioptric telescopes use more materials than the other two telescope types. Additionally, the extra materials make catadioptric telescopes heavier and more burdensome to carry around.

As a result, these telescopes may be more trouble than they are worth if you are new to stargazing.