Which telescope is best for viewing galaxies?

Have you ever seen a distant galaxy with your own eyes? Beginners usually want to get the Andromeda galaxy ticked off the list as quickly as possible, but not all telescopes are ideal for going galaxy-hunting. For that, you'll need a 'fast' telescope. Not sure what that means, or need some more information? Here's everything you need to know about choosing the best telescope for viewing galaxies.

Galaxies and the deep sky vs solar system objects

Set up any small telescope for beginners and you'll be able to get some kind of view of a galaxy before then pointing it at planets or the Moon. However, targets in the deep sky and outside of our own galaxy are incredibly dim, whereas those within our own solar system are fantastically bright, relatively speaking. So it makes sense that the telescope you need to get the best views of either of those extremes will greatly differ. For viewing galaxies as clearly as possible you'll want a 'fast' telescope.

Telescopes for galaxies: understanding aperture

A 'fast' telescope ideal for viewing galaxies is one with a large aperture that allows in as much light as possible (for planets a 'slow' telescope is fine). The aperture of a telescope is the size of the lens or mirror, usually expressed in millimetres and inches (the higher the numbers, the better). 

Telescopes for galaxies: understanding focal lengths

The focal length of a telescope is the distance from the objective lens to the focal point; short focal lengths are the best for galaxies and the deep sky because they allow the most light in and have a larger field of view. Telescopes that tend to offer the shortest focal ratios include refractors, Newtonians and Dobsonians. 

Telescopes for galaxies: understanding focal ratio

If you want to compare telescopes' 'fastness' then you can calculate the focal ratio by dividing the focal length by the aperture in millimetres to produce a number expressed as an f-stop – a bit like a camera lens. The lower the number, the better, with telescopes with a focal ratio of around f7 (or lower) considered 'fast' enough.

Telescopes for galaxies: understanding magnification

Most beginners obsess about magnification, but you really don't need to if you want to mainly study the deep sky and galaxies. You can discover your telescope's magnification by dividing its focal length by that of the eyepiece. For example, if you have a telescope with a focal length of 1,200mm and an eyepiece of 12mm then you'll get a magnification of 100x, which is perfect for viewing galaxies and the deep sky. Look for a magnification of between about 80x and 150x if you want to study galaxies and the deep sky. (Here's a guide to what you can see with a telescope with different magnifications.)