What are the Different Types of Telescopes?

Posted on August 10, 2009

There are 3 main types of astronomical telescope – and it might just turn out that the best telescope for you is the one that looks least like a traditional telescope. All 3 types have the same purpose – to collect light and focus it to a point where it can be magnified so that we can examine it. How each of the different types of telescopes does this is different, and you need to understand the differences as they greatly impact upon what it is you might want to look at, portability, cost and style.

REFRACTING TELESCOPE
These are your classic ‘long tube’ looking telescopes with a big lens at one end and an eyepiece at the other. As the light passes through the curved lens its path is bent (refraction) towards the optical axis of the smaller (objective) lens where it is bought to a focus.
Pros
*Very easy to use
*Require little to no maintenance
*Excel at planetary viewing as they are the best choice for looking at objects that have width e.g. the moon
Cons
*They are heavier, longer and more bulky than the other types
*It is incredibly expensive to make large lenses so they are limited in size and this means less aperture.
*Less aperture means that you cannot get a wide view of the sky and so they are not great for looking into deep space

REFLECTOR TELESCOPE
A Reflector, or Newtonian telescope uses a primary concave mirror that sends light to a secondary flat mirror which reflects the light out a side opening and to the eyepiece where it is magnified and focused.
Pros
*Mirrors cost a lot less than lenses meaning you get more aperture and light gathering power for your money
*Wider aperture makes for better night time viewing and these telescopes excel at viewing faint deep space objects such as remote galaxies and star clusters
Cons
*Can be fragile and sensitive
*May require regular alignment
*Mirrors require complicated cleaning and may require re-coating after several years

CATADIOPTRIC TELESCOPE
These represent the best of both worlds as they utilise both lenses and mirrors to fold the optics and form an image.  They may look the least like a ‘conventional’ telescope but they are right now the most popular type of telescope on the market. The two main types are Schmidt-Cassegrain and Maksutov-Cassegrain.
Pros
*Best all rounder – can be used for planetary, deep space and terrestrial observation
*Easy to use and portable
*Excellent optics and focussing capability
Cons
* They just don’t look like a telescope to most people
* They are more costly than other Newtonians of equal aperture

Refractor, Reflector or Catadioptric?

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