How does a Catadioptric Telescope work?

If you’re learning more about astronomy and you’re wondering about the different types of telescope that are out there, then you’re bound to come across the catadioptric system. Those that have suffered with chromatic aberration (also referred to as color fringing) will be interested in this style of telescope, as it all but eliminates the problem.

They do work differently to both a reflector and a refractor, however it does utilize the technology of both of them. Let’s look at how this type of telescope works.

How does a Catadioptric Telescope work?

Well, whilst a reflector telescope uses mirrors and a refractor telescope uses lenses, a catadioptric telescope actually uses both. It has photographic catadioptric lenses, but it also uses a pair of mirrors too.

When the light comes through the telescope, it first passes through a collective lens. This lens is there to correct the image and helps to reduce any kind of aberration that may occur and distort the final image from reaching your eyes. The light then passes through to the primary mirrors, which are curved. This reflection is then cast onto the secondary mirror, which then comes through to the eyepiece.

The name catadioptric is actually a merger of the two different types of system that this telescope uses. The word catoptric refers to the curved mirrors that the telescope uses, whilst the word dioptric is uses for the lenses of the telescope.

Catadioptric systems are used in many other inventions as well as telescopes, like in microscopes and car headlights. But the key take-away is that whilst they use a spherical primary mirror, which is common with any Cassegrain telescope, they also have a corrector lens in there as well.

Pros and Cons of Catadioptric Telescopes

Catadioptric telescopes have both good things and bad things about them that you should probably consider.


  1. The best thing about a catadioptric telescope is that it really limits the amount of aberration that may occur in your view, and it can help to ensure that you get an error-free view of the night sky.
  2. Another main benefit of opting for a catadioptric telescope is that it’s going to be a lot easier to carry around with you. They are generally lighter than both reflector and refractor telescopes, so they make a great choice for those looking for a good portable telescope.
  3. Although most catadioptric telescopes can be expensive, some of them are within a reasonable price range due to the cheap materials it costs to make it’s parts (mirrors etc).


  1. Catadioptric telescopes are generally not very heavy, and the larger aperture telescopes are not really suitable for being carried around. This is because they’re made up of heavier materials, especially when the telescope has a higher aperture – they can be in excess of 50lbs or even more than this.
  2. Like reflectors, catadioptric telescopes need quite a lot aligning and collimation when you’re using them. If you want to avoid this, then you can opt for a refractor telescope instead, as they don’t require collimation.
  3. Typically, the secondary mirror in a catadioptric telescope has been known to cause problems and obscure the vision of the the viewer. However, this is the same as a Newtonian reflector, and it isn’t really considered a problem nowadays.

Common Types of Catadioptric Telescope


Probably the most common type of Cassegrain telescope on the market is called a Schmidt-Cassegrain. This is a form of catadioptric telescope, which combines the best of a Cassegrain telescope with its reflective mirror system, with that of a corrective refracting lens.

So, the light shines through the corrective lens before reaching the primary and secondary mirrors. They’re a common form of Cassegrain, and are used by astronomers worldwide due to their relatively low build costs. They manage to deliver a solid aperture for a wide field of view.

Ritchey–Chrétien telescope

A Ritchey–Chrétien telescope is what’s referred to as a classic Cassegrain – this means that it doesn’t use the corrective lens that the catadioptric telescopes do. This type of telescope works by combining the hyperbolic primary with hyperbolic secondary, which works instead of a corrective lens, and prevents any obscurities in your view.

Common Questions about Catadioptric Telescopes

Why are catadioptric telescope used?

Generally, catadioptric telescopes are used by professionals and some amateur astronomers because they help to correct the amount of errors that you’ll see when looking through the eyepiece of a telescope.

Where were catadioptric telescopes invented?

Catadioptric telescopes date back hundreds of years in their origin. One of the first of these was founded by W. F. Hamilton in 1814, more than 200 years ago.

What is an aberration?

An aberration in an optical sense refers to the distortion or blurring of an image or view – this is what catadioptric telescopes help to minimize.

Catadioptric telescope vs Reflector

The difference between a catadioptric telescope and a reflecting telescope is that in a catadioptric telescope, light passes through a corrective lens before reaching the reflective mirrors. This isn’t the case in a normal reflector.

Are catadioptric telescopes good?

Yes, if you can afford to then getting a catadioptric telescope can be a good idea. However, you’ll probably need a larger budget than you would if you were looking for a cheaper reflecting telescope.


In conclusion, catadioptric telescopes can be a good choice if you’re looking for something lightweight and portable that you can easily carry around with you. They combine both the technology from refractors and reflectors to give you a good error free view of the night sky.

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