Types of Telescopes

Table of Contents

Reflector telescopes, refractors, catadioptrics… What do these words even mean? Moreover, does it even matter what kind of a telescope you are using?

It turns out that it does matter. Each telescope type has its own specifics that make it the best for a particular purpose. With that being said, let’s overview the purpose of each telescope type, as well as the difference between types of telescopes.

Refractors

Refractor telescopes boast a simple design that requires very little maintenance and is very reliable.

These telescopes are particularly suitable for observing closer objects lying within the Solar System. However, the specs of a refractor telescope, as well as the used accessories are going to have a significant impact on what you will be able to see.

Cheaper refractor telescopes offer decent visibility for observing the Moon, as well as for terrestrial observations. However, pick a good telescope and equip it with the right eyepiece, and you are going to see much farther into the Solar System.

The optical system in refractor telescopes is essentially a straight line, which means that there are no obstructions or secondary mirrors that would make the telescope complex and more difficult to maintain, like it is with other telescope types. Aside from that, the simple optics of refractors allows for little to no aberrations.

With that being said, refractor telescopes tend to be more expensive per mm of aperture than other types. Aside from that, their lens systems weigh more than in reflectors or catadioptrics. Lastly, since refractors tend to have smaller apertures than other telescope types, they are worse at seeing dim deep-space objects.

Overall, here are the pros and cons of refractor telescopes:

Pros
  • Require little maintenance
  • The simple lens system produces little to no aberrations
  • Greatly suitable for observations within our Solar System
Cons
  • Tend to cost more per mm
  • Tend to be heavier
  • Not as good for observations beyond the Solar System

Here are some really great examples of refractor telescopes

MAXPLATER 70mm telescope

Features & specs:

  • Inexpensive
  • Suitable for shorter-distance Moon and terrestrial observations
  • Lightweight design
  • 400mm focal length & 70mm aperture
  • 16x and 66x eyepieces


Sky-Watcher ProED Doublet APO Refractor Telescope

Features & specs:

  • Great for long-distance observations
  • Rugged design
  • 900mm focal length & 100mm aperture
  • 45x and 180x eyepieces


Orion 9005 AstroView 120ST Refractor Telescope

Features & specs:

  • Excellent for observing distant objects
  • Height-adjustable tripod
  • Smooth and stable German equatorial mount
  • 600mm focal length & 120mm aperture
  • 24x and 60x eyepieces


Reflectors

Comprised of mirrors, reflector telescopes (also known as Newtonian telescopes) offer greater value per mm of aperture since mirrors are cheaper to manufacture than lenses. However, the build of reflector telescopes is more complex.

To focus the light into the eyepiece, reflectors bounce it from a primary mirror into a secondary mirror placed near the front of the tube at a 45-degree angle to the primary mirror. The secondary mirror then sends the light to a side-mounted eyepiece.

The secondary mirror causes a slight obstruction to the light entering the telescope tube. Due to this, some light diffraction and loss occur in reflectors. Aside from that, traditional reflectors’ tubes are open to exterior elements, which means that reflector telescopes require occasional cleaning.

A variation of reflectors called Schmidt-Newtonian has a corrector plate at the front of the tube, whose purpose is to shield the tube’s interior from the elements and also reduce spherical aberration.

With that being said, reflectors can have much larger focal lengths and apertures than refractors, which allows for better deep-sky performance. Reflectors quite easily see galaxies and nebulas.

There are even the so-called Dobsonian telescopes, which are reflectors with extra-large focal lengths and apertures.  These can get very heavy and bulky, but they offer unparalleled performance for deep-space observations among any telescope type.

In conclusion, the pros and cons of reflectors are the following:

Pros
  • Unparalleled performance for deep-space observations
  • Costs less per mm of aperture than refractors
Cons
  • Open-tube designs require maintenance since they are exposed to the elements
  • Suffer from aberration and light loss

Here are some really brilliant examples of reflector telescopes:

Orion 10019 SkyQuest XT10i IntelliScope Dobsonian Telescope

Features & specs:

  • Computerized tracking with a database of over 14,000 celestial objects
  • Stable telescope base
  • 1200mm focal length & 254mm aperture
  • 48x and 120x eyepieces


Celestron PowerSeeker 127EQ Telescope

Features & specs:

  • Inexpensive
  • Light and compact for a reflector
  • Adjustable tripod height
  • Sturdy and smooth German equatorial mounting system
  • 1000mm focal length & 127mm aperture
  • 50x and 250x eyepieces plus a 3x Barlow lens


Orion 09007 SpaceProbe 130ST Reflector Telescope

Features & specs:

  • Stable and smooth German equatorial mount
  • Quite lightweight
  • Adjustable tripod height
  • 650mm focal length & 130mm aperture
  • 26x and 65x eyepieces


Celestron NexStar 130SLT Computerized Telescope

Features & specs:

  • Motorized alt-azimuth mount system
  • Database of over 4,000 celestial objects
  • Adjustable tripod height
  • 650mm focal length & 130mm aperture
  • 26x and 72x eyepieces


Catadioptrics

Lastly, there are catadioptric telescopes. These telescopes combine some of the pros of refractor and reflector telescopes, but they do have a very different design.

Catadioptrics have a folded optical path. Entering through a thin aspheric correcting plate, light first reflects off a spherical mirror at the back of the tube. It goes to a smaller secondary mirror placed right behind the corrector plate and is then reflected to the optical tube in the back. Finally, the light goes through an opening in the rear of the tube towards the eyepiece.

Due to their folded optical path, catadioptrics have short tubes with long focal lengths. The build of these telescopes also allows for maintenance-free operation. However, the use of a secondary mirror implies some light loss and diffraction just like in reflectors.

Catadioptric telescopes tend to be more expensive than similarly-sized reflectors, but they offer more mm of aperture for the money than refractors. Plus, they are excellent for deep-sky viewing, but reflectors tend to be better when it comes to observing extremely dim objects.

To summarize, the pros and cons of catadioptrics are the following:

Pros
  • Require little to no maintenance
  • Short optical tubes
  • Great performance for deep-sky observations
Cons
  • Susceptible to light loss and diffraction

Here are some outstanding examples of catadioptric telescopes:

Celestron NexStar 8 SE Computerized Telescope

Features & specs:

  • Database of over 40,000 celestial objects
  • Fully automated GoTo mount
  • Comes with 6 filters and a 2x Barlow lens
  • Height-adjustable tripod
  • 2032mm focal length & 203.2mm aperture
  • 81x eyepiece


Celestron NexStar 6 SE Telescope

Features & specs:

  • Database of over 40,000 celestial objects
  • Fully automated GoTo mount
  • Height-adjustable tripod
  • 1500mm focal length & 150mm aperture
  • 60x eyepiece


Orion 10022 StarMax 90mm TableTop Maksutov-Cassegrain Telescope

Features & specs:

  • Inexpensive
  • Very compact and lightweight
  • May be mounted to any sturdy surface
  • 1250mm focal length and 90mm aperture
  • 50x and 125x eyepieces