It is very tempting to buy a telescope from a supermarket for £129, which promises to give you a magnification of 525x. Sure enough,it will actually magnify 525x, but what you will see will be so blurred and dim that it will be utterly unrecognisable. Also, the flimsy tripod supplied with it will wobble so much that you will get motion sickness within minutes.
So what do you need to keep in mind when buying a telescope? Well, the answer is not that simple, but there are a few ground rules. If you keep these in mind, the chances of getting the scope you want will be greatly increased.
Rule 1: The more you pay, the better the scope
Some people will disagree and I must admit that this rule doesn't always apply. Sometimes you can get a very good scope for less than you expected to pay. However, quite often, a more expensive telescope of equal aperture outperforms it in at least one or two aspects. What I am really trying to say is, the less you pay for the scope, the less you should expect from it. No problems.
Rule 2: Size matters
In our example of the supermarket telescope, you are led to believe that the scope is suitable for a magnification of 525x. This, however, is not important at all. Many telescopes will allow you to do that, the question is what the image looks like at that magnification. Well, to get a decent image at 525x, you are typically looking at a telescope that will cost you around £1200 upwards. Why? Because the scope will need to have a so-called aperture of at least 250mm (10 inch). The aperture is the unobstructed diameter of the telescope's main lens, or mirror, and the bigger it is, the more you can magnify the image without causing it to deteriorate. Furthermore, quite often you don't want, or need, high magnification. What you most often need is the ability to grab light, as astronomical objects tend, in general, to be very dim. Again, the bigger the aperture of the scope, the more light it will gather and the dimmer the objects you will be able to see. However, size comes at a price and, usually, the bigger the aperture, the more expensive the scope.
Rule 3: The best scope is one that is used often
So you’ve spent £3000 on a scope but it is so big and heavy that you need 2 people to set it up, not to mention the time it takes you to get it into your vehicle. This is because you need to travel 10 miles to the nearest dark sky location. That might not be a problem but what if you live on the 4th floor in a high-rise? How often do you think you are going to use the scope? The lessons to learn from this rule are many. You need to think about where you live and where you are going to use the telescope. If you live in a location where you can put the scope in a permanent observatory, by all means go for something big. If you need to travel a lot, try to get something compact, light and easy to set up.
Rule 4: Features don't improve optical quality
A telescope that hops automatically out of its box and starts looking at objects in the sky for you is not necessarily of high optical quality. Yes, those automatic, so-called ‘go-to’, type of telescopes are very easy to use, but there are a number of disadvantages. You need power, although this is usually supplied by batteries. They are not necessarily cheap, although you can get some low cost ones, but the optical quality is average and their aperture usually very restricted. And you won't learn about the stars! If the scope is doing all the work, why not get some photographs out?
However, the flipside is that a big scope with few features, such as a so-called Dobsonian telescope, usually restricts its use to visual observation only. If you plan to take photographs with your telescope, make sure you get the type of mount that will allow you to do that.
Rule 5: Try before you buy
There are many different types of telescopes on the market, so how do you know which one is the best for you? Well, it really depends on your interests. Each type of telescope has its own merits and restrictions. Refractors can render incredibly sharp images but are usually limited in aperture. Large aperture refractors are expensive and tend to have long focal lengths, making them them less suitable for widefield work at lower power. Reflector telescopes provide relative more aperture for your money but, due to the so-called secondary obstruction, images are usually not as sharp. However, they are usually much better suited for deep space widefield work and for photography for beginners.
So what is the best scope for you? Well, why not try some out before you decide? This is easier than you might think. Join your local Society and go to their star parties. During those observation sessions you will usually be able to try all sorts of different scopes on all sorts of different objects in the sky. You will also be able to ask all sorts of questions, of course.
Rule 6: Buy binoculars
Well, this is really for those of you that are absolute beginners. The problem with most telescopes is that they are usually much less easy to use than you would think. Finding your way around the heavens by looking through a tube which only shows you the tiniest fraction of sky at a time, often with an upside-down or left-right swapped image, is anything but easy.
With a simple set of 7x50 or 8x50 binoculars, you can see lots and lots more than you can see with the naked eye. Binoculars are very easy to use and help you to learn to look through an optical aid. The quality of a telescope is not the only thing that makes it a useful instrument, as even the best telescopes are useless in the hands of an unskilled observer. Binoculars are excellent ‘trainer scopes’.
Once you have decided to buy your first telescope, don't just buy it from the cheapest place; buy it from the shop that gives you the best service and advice - it enhances the experience and makes a good contact for future purchases.