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Thinking of buying a telescope?
Things to consider before you buy
Reflector Telescope … Refractor Telescope So, here’s the general advice.
Telescopes are rated by their diameter (not magnification, in fact if you ever see a telescope promoted by how many times it magnifies then avoid it as they are preying on a common misconception and that usually tells you a lot about the ethos of the manufacturer).
There are two types of telescope:
Refractors, that use lenses to form an image, and
Reflectors, that use mirrors
For various reasons a mirror should be about one-and-a-half times wider than a lens to give the same view of an object.
The minimum size of reflector for serious use should be about 6-inch (150mm).
Although a little bit smaller than this (don’t go below 100mm) will give good views of the Moon and the odd bright comet or some of the ‘deep sky’ objects (star clusters, nebulae or “gas clouds”, galaxies and the like).
However, a 100mm and 150mm reflector will probably be on the same mount, use the same eyepieces so there is little saving in going small. Save a little bit harder and wait until you can afford a 150mm. I’ve seen detail on the surface of marks (ice caps, dark surface markings) with a 150mm reflector.
Of course, if you can go for a 200mm or even larger scope then they are very much more powerful.
Remember if you increase a telescope’s diameter by half (e.g. go from 100mm to 150mm) you get a view more than TWICE as good.
The above size recommendations (150mm minimum) for serious viewing) are for reflectors.
The equivalent refractor would be 1.5 times small i.e. 100mm.
The problem with refractors is that they are expensive to make in large sizes.
Thus most big telescopes (and all the professional telescopes in the world) are reflectors.
However, refractors are more compact and in small sizes they take up less room and don’t cost much more than reflectors, so you’ll see a good range of refractors from 70mm to 150mm on offer before the price becomes exorbitant.
Refractors can be used for daytime work as well as they usually have a ‘diagonal’ that gives an upright images (astronomical telescopes normally give an upside down image) which is something you may want to consider.
Astronomy Ireland’s Andrew Langton has done a great breakdown on individual scopes available HERE
There are special types of telescope that use both mirrors and lenses, such as the Maksutov design, or the SCT (Schmidt Cassegrain). These are normally quite expensive, costing twice or more of the equivalent reflector. But they are a good investment as they last a lifetime if well looked after, and they take up a lot less space (the tubes can be 2 or 3 times shorter than the equivalent reflector). A lot of ‘serious observers’ use them for the convenience of not having to build an observatory for a large bulky reflector or to take them to dark sky sites around the country for even better views. If you’ve got the budget for one of these you probably don’t need all this advice. Expect to pay over 1,000euro at 2016 prices.
The stand that the telescope comes on should be considered too. Especially in smaller cheaper telescopes where the maker is trying to keep the price low. A flimsy stand will shake in the wind and even when you touch the telescope to focus for example. For serious work make sure the stand is sturdy or you’ll find it hard to use the telescope.
These days there are ‘go to’ or computerised mounts. They usually add a few hundred euros to the price for all the motors, software etc needed to drive them but they make your telescope extremely effective by not only being able to find dim objects easily, but also tracking them and keeping them in the field of view as the Earth rotates.
This can vary widely as we’ve covered a lot of telescopes above, from beginners telescopes (100mm reflector or 70mm refractor) to hybrids on computerised mounts. So prices can range from under 100euro to over 10,000euro. (These prices are a very rough guide as at 2016).
But most people will probably spend a couple of hundred euro on a good telescope.
You can get a beginner one for the Moon and very casual viewing for under 100euro but you’ll always want more if you view regularly.
If you do not get a computerised telescope 200 to 500 euro should give you a wide selection of models to choose from.
500 to 1,000 euro should get you a decent sized telescope (150mm reflector, 100mm refractor) on a computerised mount.
Anyone spending above 1,000euro probably does not need this beginners advice.
So, you’ll probably get a reflector (150mm or larger) or modest refractor (100mm or so).
A manual mount will end up costing 200-500 euro and a computerised one 500-1,000 euro.
These are telescopes capable of some serious viewing so do write and tell us what you see for inclusion in Astronomy Ireland Magazine’s monthly round up of Irish astronomy.
MAGAZINE IS VERY IMPORTANT
Subscribe at www.astronomy.ie/magazine before you get the telescope as it will tell you what sights to see with the naked eye, binoculars and small telescope in Irish skies every month. It’s also much more fun being part of a large community of like-minded individuals rather than viewing on your own.