So, you're ready to buy a telescope or upgrade to a new one? Here is a very frank explanatory guide to telescopes, including my personal recommendations.

Telescopes Do Not Magnify!
Telescopes do not magnify. I know, you've seen in the shops the Amazing Power of such and such a telescope, and are impressed. But in truth, telescopes do not magnify. I'll explain.

A telescope is a giant eyeball. It collects light using lenses or mirrors or both, but its chief function is to be a light bucket. I tell people that if money were falling from the sky, would you rather have a coffee mug or a rubbish bin to collect it in? The bigger the bucket, the more you can get in it: telescopes are no different.

The magnification power comes from the little eyepieces that you slot into it. (Please see our Eyepieces and Filters Guide for more detailed information.) These are magnifying glasses of different strengths. You can magnify the image the telescope has collected hundreds of times. But if the original image was pants, then the magnified image will be even worse.

In our "raining money" analogy, you could stretch the amount of goods you could buy with the coffee mug's takings, but the quality of those goods would be poor compared to the posher goods you could get with the bin's takings. For telescopes, if you get more light, you get more to magnify, and your images are far better.

The bucket size of a telescope is called its aperture. The bigger the aperture, the more light that comes in. So if a telescope advert is saying the telescope is a "60mm", it means the bucket is just over two inches across. If it says the telescope is "an 8inch", it means the bucket is eight inches across! Both telescopes can advertise that they magnify hundreds of times, but which will have the quality view?

In summary, although bigger does mean better in telescope apertures, I am not telling you that smaller telescopes are not worth purchasing. I just wanted you to know that you should never be impressed by a telescope's advert just because it says it can magnify hundreds of times. Ignore that entirely. Here instead is what you want to look for as the marks of a quality telescope -- of any size -- that you would get a lot of use from:

Good Optics
In general, a telescope that you buy in a grocery store is not going to be made to the same quality as one you would buy from a camera store. It will work, but you will get limited use from it. This is because its optics will not be very good.

Typically, the most common store-bought telescopes are the long, thin tubed ones. We call them refractors, because they refract (bend) light through a lens to get it to focus at the end of the tube. Some light gets lost when it passes through any glass like that, similar to raking the lawn and catching a bunch of leaves in the tynes of the rake. Therefore, lensed telescopes will always lose light. However, a good expensive lens can deliver a crystal clear image.

Bad lenses have been ground quickly and in a way that makes their outer parts nearly useless. Good lenses have been ground to use the entire glass well and often include another lens nudged up to it that helps shepherd light from the edges back down into the tube. You will pay dearly for a good refractor, because they are hard so hard to make.

Mirrored telescopes, called reflectors, can be made quickly as well, but do not suffer from permanent problems like the lensed ones. They can show a different kind of poor workmanship, bad mirror placement and poor coatings, but they are fixable.

If the mirror is placed in the tube badly, the result will be the same as a bad lens: it will lose light from the outer parts. However, using a process called collimating, you can tune your telescope's mirror back into place. Most reflectors come with a set of screws on the back of the mirror for exactly this purpose. Some observers collimate their telescopes every time they go outside, but it's not strictly necessary. Any astronomy club will have members who can help you with this until you learn to do it yourself.

Mirrors also can lose their reflective coatings. You've probably seen this happen around the edges of your bathroom mirror. I've had my reflecting telescope for over ten years, and the mirror is still fine. But in another ten years' time, I may need to get it re-coated.

Some very expensive telescopes use a combination of lenses and mirrors to give an outstanding view in a small package. They are called Catadioptrics, or Cats, and smaller versions are often used as spotting telescopes for birdwatching.

All Cats fold their light inside them using three mirrors and a correcting glass. The correcting glass is needed, because the mirror is a portion of a sphere. Spherical mirrors are cheaper to make, but they spray their light at the edges like a lens. The glass plate helps prevent that from happening. Clever.

The classic Cat is the Celestron 8-inch Schmidt-Cassegrain, the "C8" as we call it, and it was 70s orange. Cats are now motorised to stick with the stars, and most include onboard computer navigation, like their own GPS of the night sky. All you have to do is punch in the name or coordinates, and the telescope runs itself. Of course, you have to polar align it first, which can put a lot of people off. (Read our Using Your Telescope guide for more information.)

Many other types of telescopes are also out there, but these are the basics that you will find easily available to you.

In summary, a cheap, mirrored telescope will give you a better view than a cheap lensed one -- chiefly because the mirror will be larger.

Good Mount
I have never been more frustrated with a telescope than when I've been fighting with an awful mounting under it. Rickety legs and tedious gearing can drive me insane. I've known too many people who've tried once to work such a telescope and have given up and shoved it into a closet forever after. 

Too many of the small refracting telescopes come with a rickety mount. In truth, it is a scaled down version of a professional mount that astronomers use. The mount type I'm talking about is an equatorial mount. It is a mount that you can set to the equator of the Earth and to the North Pole of the night sky (See our Polar Constellations guide for more information). In this way, the telescope should move the same way the stars do, and so you can keep focused on any object with just tiny twists of a gear knob. On paper, this is an excellent mount.

As I said, however, this is how the professionals do it -- but with one difference. Professional astronomers have an observatory where the telescope's mount is cemented into the ground and permanently set to the Earth's equator and Polaris. A portable telescope needs setting up every time you walk outside with it. And its mount is not nearly as stable.

If you have the knowledge of the night sky, the patience to set it up correctly and no small children or pets who will knock the mount, then go ahead and buy a telescope with an equatorial mount.

An Alt-Az mount is simpler. It moves the telescope side to side and up and down. A telescope on an Alt-Az mount needs no setting up, and so it is faster off the mark. The tripod type of Alt-Az mount can be rickety, and you will need to be sure you've locked off the legs tightly to keep your image from bouncing.

A Dobsonian mount is a type of Alt-Az mount. The Dobsonian works on a spinning table idea, like those you may have seen at a Chinese restaurant. The reflecting telescope sits on the turntable, so it can turn completely around. It is balanced in a box frame with swivels cut in, so that it can rock up and down like a see-saw. A Dobsonian is the sturdiest mount of any of the telescopes.

For those who want to know, Alt-Az stands for Altitude-Azimuth, the astronomers' terms for height and degrees around the horizon from north. In using all Alt-Az mounts, you do need to get familiar with how objects will glide through your view for how to move the telescope to put it back into view. The equatorial mount, when set up correctly, moves the telescope via turning knobs. For keeping up with an object gliding out of view, you need only turn one knob. Some mounts are equipped with a drive on them, so that the telescope moves on its own. These are terrific if you know how to align them to Polaris and other stars every night.

In summary, a sturdy mount such as a Dobsonian or a chunky tripod with Alt-Az mount will keep your telescope steady for a better viewing experience. Avoid an equatorial mount if this is your first telescope. And avoid a flimsy tripod if you have children or outdoor pets.

My Recommendations
If you want to buy a telescope for a child under the age of ten, then I recommend the Infinity-76P from Sky-Watcher. It looks like a little blue plastic toy, but is in reality a nearly indestructible reflector of 3 inches across. This is the same size as most refracting telescopes you see on the shelves in grocery stores, but instead, this reflector sports good optics, a sturdy mount and out-of-the-box instant use (it comes with its own eyepiece). I own the American parent of this one, a 1978 Astroscan. It has travelled with me all over the world.

If you wish to purchase your first telescope or a telescope for someone who has a budding interest in astronomy, you cannot go wrong with a 6-inch Dobsonian like Sky-Watcher's Skyliner-150P. It is easy to build, simple to use, and will give you excellent images through its two included eyepieces. In this way, it will not discourage any interest you or a loved one has, and may even inspire a career in space science or engineering!

If you are looking to build a backyard observatory, then the best option is a Schmidt-Cassegrain. They are compact, stable and have terrific optics. If you are on a budget and want a no-frills Cat, then you cannot go wrong with the old C8 I mentioned above. If you find a decent one on eBay, grab it. If you want an all-singing, all-dancing scope, then go for the larger newer models made by Celestron or Meade.

For Advanced Observers
I did not include specific information in here about focal lengths, exotic mounts or focusers. I figure that if you know enough about those features, you probably don't need my help!

(For the record, I'm not affiliated in any way with any products or companies described above. The Sky-Watcher series, however, has been tested and endorsed by Sir Patrick Moore, and I have recommended them to many National Space Centre visitors. We sell them in our shop, if you want to come have a closer look.)