Your first telescope

Buying your first telescope can be a terrible experience. There are so many out there. And so different. And all these numbers. Want to know what to look for and avoid buying the marketing humbug instead of the real thing? Read on if you want to know.Size matters, honeyFirst of all realise what is the main function of any telescope. Mind you it's not magnifying - even if the marketing people would like you to believe so. No - the telescope's main function is to gather light. Grasp as many photons coming from that faint and whispy nebula dozens of thousands of light years away. Or the ones coming from a galaxy billions light years away. Some of these objects are the size of the moon or even a lot larger. So ... you don' t need to magnify them. It's the difference between your eye's pupil (dilated at night to something in range of 8mm) and the telescope objective or mirror diameter (also known as the aperture). It is this diameter that is responsible for gathering light and pumping it to your eye (and as for the pumping.... never attempt to look at the sun with any kind of device that has not been designed for such purpose. Telescopes, binoculars will pump all this energy down into your brain frying the eye on the way there). And if you see a 70mm telescope advertised to magnify 700x (even, or especially when it is outfitted with barlows and eyepieces to that effect) go elsewhere. A very simple rule of thumb for maximum magnification is that for any given aperture the maximum magnification you can get on a good night is slightly more than twice the aperture diameter in mm (three times for good and pricey apochromatic refractors). So that 70mm scope will go up to about 150x magnification. After that you will just see a bigger blob with less details.The next big thing - who you are, where you are, and what you want to look atAnd this is where simplicity ends... after all, there are so many different types of scopes out there. Various constructions. Various designs. So what is the next determining factor. It is what you want to do with the scope. If it is to go after that good looking neighbour buy small azimuth mounted refractor. It will also show the Moon and it's craters, and if you are lucky you might spot Jupiter and the galilean moons before they put you in for spying on other people. But if you are serious about looking at the sky think of how you want to observe. Are you going to look at the sky, or do you want to eventually photograph it. Where are you observing from. Do you have to drive 50 miles to get a clear, black sky. Or do Milky Way shines in your backyard? Looking at these issues will help you decide first about the mount of the telescope and then on the type. If you live in a city, and need to drive to countryside to see black sky you will want a portable telescope of smaller size, and less weight. If you are lucky to have Milky Way as the only neighbour in your backyard you may be better off with something much larger. If you do not plan on doing any astrophotography - a huge aperture telescope on a dobsonian mout is the best way to go (and for the citydwellers you might consider truss-tube dobsonian which will not make you choose between a scope and friends or family). If, on the other hand, you want to go into astrophotography eventually - think about equatorially mounted scope that you can add motors to at some point. Nice looking GoTo telescopes on the altazimuth mount (the fork type, or assymetrical fork) are... suprise... not so great for astrophotography if they don't come with something called equatorial wedge, and... not so great for visual observations since you pay huge lot of bucks for the electronics and get a small glass to go with the 40,000 object database (out of which you may actually be able to see 50 or 100 objects). So you are probably better of with a simple reflector (for visual) or refractor (for photographic) on a simple equatorial mount. Just make sure it is a sturdy mount. The best telescope on a flimsy mount will show you nothing but wobbling, hopping and whizzing blips of light with no sense.Long, medium or shortAnd finally the construction. If you want high contrast, high magnification images of planets - forget newtonians and get a long refractor or a maksutov. But also forget the deep sky wonders. But remember - there are less then ten interesting objects you will be able to observe visually with an average telescope of this type. So, unless you are are planetary freak go elsewhere. If you do not care for high contrast, but want to SEE more of the deep space - buy aperture, buy a newtonian reflector. It is usually huge, uncompromising, making your trips to the country in one car a thing of a past ;). There is also a third way - a short refractor. These have been either expensive or optically inferior in the past but recent technological advances made designing them easier and the new ones are usually great - more compact than either long refractors (with usually tha same amount of chromatic distortion) or newtons (with better constrast and sharpness than newtons). And if you have a heap of money and want a big and compact telescope consider a Schmidt-Cassegrain. But only when you know that spending nights outside is something you really wnat to do for the rest of your life :)