Choosing a telescope
Choosing the right telescope from the myriad available can be a much simpler matter than it would seem at first glance. A few simple steps will quickly allow you to “home in” on the type of instrument most suitable for your purpose.Firstly, are you sure you need an astronomy telescope? If the person who will be using the instrument has no interest in astronomy, then you will be better off going back to the main menu on the left and clicking on 'Spotting scopes' – the instruments offered there are all suitable for normal daytime (or terrestrial) viewing and will provide the best views of birds and other wildlife as well as general target spotting (ships and just general interesting stuff going on around us). Of course, any spotting scope can be used to observe the craters of the Moon and many of the more prominent features of the brighter planets.
But if the telescope is to be used for astronomy as part of the primary reason for purchase, then stay in this section and read on.
Find the right telescope quickly.
To find the best telescope as quickly as possible we recommend that you simply use the selection tool at the top of the main page to restrict the view of instruments to only those that are most suitable for your particular needs.
If the telescope is required for the viewing of both astronomy and terrestrial targets on a 50/50 split, then use the selection tool to restrict the view to telescopes capable of terrestrial and astronomical use. The telescopes displayed will be first and foremost for astronomy but will all be of a type that make them suitable for terrestrial use as well.
If you are buying an astronomy telescope as a gift to introduce someone to the hobby of astronomy who has not owned or used a telescope before, then use the selection tool to restrict the view to telescope for adult gift or telescope for child’s gift. In each case you will be offered telescopes that have been selected with the needs of the first-time user in mind. The telescopes will be easy to operate and fun to use.
A telescope makes a wonderful gift for someone who has even a modest interest in the night sky. Even our smallest astronomy telescope is capable of revealing the craters and mountains of the Moon, the rings of Saturn, the cloud belts of Jupiter, hundreds of star clusters and even distant galaxies.
Want to know more about telescope types?
There are several different types of telescopes to choose from. Each type has their advantages and disadvantages.
Telescope (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') is an instrument designed for the observation of remote objects.
A refracting or refractor telescope is a dioptric system that uses a primary lens to form an image. Importantly, the light passes through the lens and is not reflected by it. The refracting telescope design was originally used in spy glasses and astronomical telescopes, but is also used in other devices such as binoculars and camera lenses. The refractor is really the traditional type of instrument that everybody instantly recognices, You point one end to the target and look through the other end – nice and simple!
A typical refractor has two basic elements, an objective lens (or more commonly group of lenses) and an eyepiece. The objective in a refracting telescope bends light rays to form an image that is then magnified and delivered to the eye by the eyepiece. This allows the user to view the image of a distant object as if it were clearer, and larger (in fact it appears to be nearer). Refracting telescopes can come in many different configurations to correct for image orientation and types of aberration. Refractors used exclusively for astronomy always show either an inverted image, or (if a star diagonal mirror or prism is used) and image that is the right way up but flipped left to right. This is not regarded as a disadvantage in astronomy as the concept of “right way up” has little relevance in space away from our normal frame of reference.
The reflecting telescope is an optical telescope which uses a combination of curved and flat mirrors to reflect light and form an image. British scientist Sir Isaac Newton created the first reflecting telescope around 1670. He designed the reflector in order to solve the problem of false colour called chromatic aberration, a serious problem in the telescopes of the time before the perfection of achromatic lenses. The traditional reflecting telescopes that we sell are known as Newtonian reflectors. They are usually of good to excellent optical quality and have the benefit that they are cheaper to manufacture in apertures over 100mm when compared to refractors.
The mount and the myth of power
The mounting used to support a telescope turns out to be at least as important as the telescope optics – in fact, probably more so, because no matter how good the optics of a telescope are, if you can’t hold the instrument steady enough to make useful observations it may as well be worthless. Any problem with the mounting of the telescope is simply made worse as you increase the magnification. Remember: when you are observing at 50 to 100 power, any movement or vibration of the telescope will also be magnified 50 to 100 times! There's not much hope of seeing detail on planets or the Moon when they're whizzing around in the eyepiece like demented fireflies!
The myth of power! Here’s a puzzle: the worlds largest telescopes are truly enormous with mirrors large enough to park half a dozen cars on, and literally hundreds of times bigger than our smallest telescopes. And yet the practical resolution (the detail you can actually see or photograph) with these monster telescopes is only about 3 or 4 times better than a typical small astronomy telescope. Why?
The answer, quite simply, is air. The thick layer of gas that surrounds the Earth sets an upper limit to the amount of resolution, and therefore the amount of magnification that can be usefully employed on any telescope. So sure, mathematically, you can enlarge or blow-up the image of any telescope almost without limit – but beyond the resolving limit set by the seeing conditions (air quality) and the resolving limit set by the telescope's maximum aperture, all you will see is a blurred image with no additional detail - bigger to be sure, but more blurred and dimmer.
The general rule with telescopes designed for astronomy is that they are capable of sustaining 50x to 60x magnification per 25mm (1”) of aperture. Many telescope sellers use the word power to imply that the more powerful a telescope is, the better it is - and that's just not true. You'll see 600x power printed in big letters on the side of a telescope box or in a newspaper advert and it’s easy to be taken in. In fact, most astronomers in Britain rarely use more than about 250X on any given night, and generally they use less than 100X most of the time.
When looking for a telescope, don't worry too much about power - what's more important is the overall quality and diameter of the main lens or mirror, ie what is known as the "aperture". The aperture of a telescope is like the engine of a car – it drives everything. All the significant features of a telescope are legislated by the primary aperture. The light gathering power - so important in collecting light, so that you can see faint objects that are vast distances from the Earth - and the resolution - important in determining the detail that will be visible when observing planets - are both determined by the telescope’s aperture. Size does matter, in telescopes - if quality was equal, then bigger would be better.