Telescope Basics

Telescopes are those things you look into and see stars, planets and galaxies up close, oh my!  Their primary function is to gather light and bring it to a point where humans can easily make out the resulting images.

But did you know there only three fundamental types of optical telescopes?  They are refractors, reflectors and catadioptrics.  More on that in a minute.

A few things first:

Image quality

The quality of the image you can see through any telescope is a function of the device’s light gathering ability or “aperture” size.  Aperture size is the size of the lens or mirror inside the telescope that points up at the sky and is the number one most important part of any telescope.  The larger the aperture size the better the light gathering and higher image quality you will get.


Magnification is how much you can blow up the image quality.  If you have a high magnification on a small aperture size the image quality will suffer.  So a good rule of thumb is to try and get a larger aperture size if you can vs getting a telescope who’s primary attribute is a huge magnification factor.

Types of Optical Telescopes

Alright, back to telescope types:

  • Refractor – A refractor telescope use a lens to gather and focus light; this was the first type of telescope ever created.  Generally these are good for objects closer to Earth such as the moon and planets in our solar system but not great for deep sky objects like galaxies.

    How a refractor telescope works

    How a refractor telescope works

  • Reflector – The reflector telescope type uses a mirror to gather and focus light.  Reflectors are better at capturing faint deep sky objects like galaxies and nebulae but not good for closer objects.

    How reflector telescopes work

    How a reflector telescope works

  • Catadioptric – Catadioptric telescopes use a combination of mirrors and lenses to form an image.  At this point they are the most popular type of consumer telescope.  Catadioptics are great for lunar or close object observation as well as deep sky viewing.

    How a Catadioptric telescope works

    How a Catadioptric telescope works

Other Types of Telescopes

  • Radio – Telescopes used primary to gather radio signals from  outerspace (satellites and probes)
  • X-ray – These are used to observe things like gamma rays and must be placed into orbit around Earth since our atmosphere blocks most X-ray waves.