Article about telescopes as first published in The Shetland Times

 

 

You want to look at the stars, gaze at the galaxies and mooch around the Messier objects.

You want to buy a telescope!

Well no.

You don't.

Buy a pair of 8x42 or 10x50 binoculars, a star chart and a basic astronomy book. Spend time finding your way around the night skies. Enjoy the freedom of being able to go outside and look at the sky without having to drag out lots of cumbersome and expensive equipment.

You already have binoculars?

In that case spend your money on a tripod and an adapter to fix your binoculars to it. You'll see twice as much as you do when holding your binos in cold shaky hands.

You are still definite you want to spend your hard-earned money on a telescope - read on for a very personal view.

A telescope for astronomy consists of four parts. Deficiencies in each of the four parts will affect the how well the telescope does its job.

 The tube assembly. This is the type of telescope. There are three main types on the market. Reflector, Refractor and Compound. They all have things in their favour and things against them. So lets think about what the telescope has to do.

 Light comes from astronomical objects and usually travels thousands of light years. It is faint and you want to get a ringside seat. Therefore, what you need to do is collect as much of this light as possible. The easiest way to do that is to have a telescope with the largest aperture you can get. The aperture is the diameter of the front lens or the width of the main mirror. Conventionally the aperture of a telescope is quoted in inches. So the more inches the more light. Even more important the more light the more you can magnify the image of the object you are looking at.

 Eyepieces are what are put into the tube assembly to magnify the image.The minimum magnification for a tube assembly is 4 times the aperture in inches and the maximum magnification about 50 times the aperture in inches. Outside these limits the system is just not efficient. The most comfortable magnification is about 75x to 120x for most telescopes.

 The mount. The 'tripod' on which the telescope sits allowing it to move easily to look at different parts of the sky. There are two types, alt-az and equatorial. The alt-az gives the same up and down and side to side movements as a camera tripod though it may look nothing like one. The equatorial mount is set up parallel to the Earth's axis and is good for high power views of planets or astrophotography as it is easier to follow objects as the Earth turns.

If the mount is not rock solid then it does not matter how expensive the tube assembly or eyepieces because every little movement will cause it to wobble. Every breath of wind will cause the image to slip out of your view.

Portability. Unless you are able to set up an observatory you are going to have to move your telescope out from under the stairs each time you use it. So the bigger it is the less you will use it. It doesn't matter if the tube assembly has an aperture large enough to see Pluto, the eyepieces give a bright image from one edge to the other and the mount is so solid that a mid winter hurricane would not cause the image to move. If you cannot get your kit outside easily then it will not get used. Eventually you will buy a pair of binoculars and use them to the refrain of..."I'd get the telescope out but it might cloud over before it is ready to use...so I'll just have a quick look through the binoculars and then go in for a cup of cocoa". The bigger and heavier the telescope the better it is at collecting dust and memories of when you last used it.

 

There are lots of considerations to take into account so lets look at some examples that can help in coming to a decision.

If money is a major factor then the choice should be a reflecting telescope on an alt-az mount. The entry-level design is usually a 6 inch aperture Newtonian reflector on a dobsonian mount with a couple of eyepieces and a finderscope. If you have a bit more money then get some more eyepieces to go with your 'scope. The alt-az version is light, easy to set up and use. You use it like big binoculars going from one object to another. The equatorial version, with a motor, will track the movement of the sky allowing high power views to stay in the field of vision longer or even some astrophotography. Nevertheless, it is heavier and takes more setting up for the same size tube assembly.

With a bigger budget you have a wider choice. If you want ultra portability and a fine telescopic view then there are several 3" refractors on the market. You will not be able to see as faint as the 6" but what you do see will have better contrast and will look sharper. Planetary observers prefer refractors.

If you want a telescope out of a box then a compound telescope might be the answer. They are small and fat and come with a stable equatorial mount. Some even have computer control for finding all those objects you have heard about and many that you haven't. They are not too cumbersome to set up but do take time.

There are some telescopes to try and avoid. Reflectors with a 3 inch aperture. Buy one and it will be good for one winter. Next year you will want something bigger. If you are unsure if observational astronomy is for you then the 3 inch reflector might be a good idea because you will have not lost too much money when you sell it on.

Those little 300-power plastic telescopes, sometimes on a nice looking wooden tripod. One company calls them 'Funscopes'. My experience is that you will have lots of fun trying to find anything through them. In my opinion you should give them a wide berth. The only use I have found for them is for projecting images of the Sun.

By the way do not ever look at the Sun through a telescope or binoculars. Unless of course you wish to go blind. Most of the filters supplied with telescopes for looking at the Sun assume you either wish to be blinded as the glass cracks and splinters into your eye or the heat of the Sun breaks through to cook the back of your eyeball.

To summarise. Go by a pair of binoculars. You can then save up for that nice 6 inch f6 Newtonian on the equatorial mount which comes in a wooden box.

Costs for all this are in the area of 100 for binoculars though reasonable quality can be bought for less. A 6 inch reflector on a dobsonian mount is about 375 and on an equatorial mount about 500. A small refractor will cost you about 450 and a 10 inch compound telescope about 1300.

 

My thanks to John Squires of Broadhurst, Clarkson and Fuller for helping with the prices and the pictures.

 

But remember the most important item that money cannot by is clear skies

 

 

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