Magnification Doesn't Matter

Abstract

Some basic pre-telescope advice is offered for newcomers to the hobby of observational astronomy.

Keywords: telescope, magnification, buy, purchase, resources, astronomy magazines, astronomy books

Introduction

Anybody with an interest in astronomy wants to immediately rush out and buy a telescope; it's only natural. But one can – indeed should – travel a long way down the road before having to plunge in and spend up large on a telescope of your own.

Maybe money's no object: ok, in that case buy whatever you like. Otherwise, though, put in as much legwork as you can stand, before you make that big purchase.

At the very least, the experience will help you refine the kind of telescope you want to own. At best, it will be a rewarding experience in its own right, and an opportunity to fully explore your own commitment to the hobby before finally settling on a budget for various flash accessories. Suppose you spend $500 (or whatever it might be) on a telescope today. If you lose interest in 3 months time, you'll regret having spent anything. Yet if your interest in astronomy becomes a consuming passion, you'll regret not spending more. So take the time to find out.

If you've ever hunted around a few general stores - department stores, camera stores and the like - you'll have seen them: beautiful sleek telescope barrels mounted on light-weight camera-style tripods, with enticing colour images of Saturn and the Orion nebula on cardboard stands, and signs claiming 500 times magnification.

Forget it. Forget it all.

The human eye is sensitive to colour only when the light is very bright. Look at the Orion nebula even through the 10 metre telescope at the Keck Observatory and it will look pale white, possibly with a hint of green, barely imagined. You will not see the bright colours of the photographic images through your own telescope with your own eyes; it just will not happen. You require filters, photographic equipment, long exposures, dark skies, experience, and a lot of patience to produce images like that. You won't see them. Get used to it.

Next, the tripod. Unless you know exactly where to look, and exactly what you are doing, a wobbly, hand-aimed camera tripod is unlikely to allow you to see anything. For the novice, a good mount is probably more important than a good telescope. It must be sturdy. When the telescope is mounted on it, there should be almost no vibration and certainly no wobbling. There should be gear-driven guidance controls (unless you're looking at a Dobson-mounted Newtonian, which I've never tried myself; if you're looking at one of these I highly recommend you test drive one before buying). The guidance controls, whether motor or manual, must operate absolutely smoothly, and of course it goes without saying that they should move the telescope without rocking the mount.

A motor drive is not absolutely essential, but it certainly allows you to forget about keeping your objects centred and concentrate on what you are seeing. I'd certainly spring for one if you can possibly afford it.

Finally to the telescope itself. What is the function of a telescope? In fact the function depends upon the use to which it is being put. Novices are often surprised to learn that, for many purposes, the primary function of a telescope is not magnification: it is gathering light. Many distant astronomical objects - star clusters, nebulae and the like - are quite big enough to see with the naked eye. The reason they can not be seen, is because they are too faint.

If anyone starts talking about magnifying power, it’s an almost sure sign they don’t know their stuff. A “real” telescope buff will talk about aperture first and foremost. Aperture is essentially how big the business end of the telescope is. The bigger the aperture, the more light it lets in. This is important because, what most novices don’t realize, the main job a telescope does is to make dim things brighter. No matter how much you magnify it, a star will never be anything more than a point of light; the key thing is to “capture lots of light” so you can see all the faint stars. Exotic things like galaxies, nebulae and star clusters are often actually quite big – they’re just too faint to see with the naked eye. Planets are a slightly different kettle of fish, because you do actually want to magnify those. But whenever you use a lens to magnify something, you also make it fainter. Therefore, even for viewing planets, it pays to gather a lot of light using a large aperture.

In the end, for most of us, it all comes down to price. Perhaps you can't afford a new, computer-guided 20 cm Schmidt-Cassegrain from Celestron or Meade, or one of those gorgeous Astro-Physics refractors. (I sure as hell can't.) Probably your only choice is to compromise on a less expensive model with a few short-comings, or go without altogether. Well that's fine, and it is not my intention to put you off. All I am trying to say is that there is a minimum quality point below which it is simply better not to purchase (buy a pair of binoculars instead; but not an easy thing to explain to a child) and to get good advice. Hopefully the foregoing will at least provide you with enough background to gauge the quality of the advice you are being offered at the point of sale. If some dick-whacker comes sliming his way across the shop-floor, prating on about magnification, you'll know to turn-tail and get out of there.

Wow, that was a bit of a rant. Why so sore? By now you've probably read through a good few astronomy magazines and have a general idea of what you're looking for. (If you haven't, then please read my earlier article.) So you won't need to be told that the finder-scope and eyepieces sit up the business end of a Newtonian. One day I found myself in a particular camera shop, picking up a film, when I noticed a Newtonian aimed at the floor. I discretely suggested to the gent behind the counter, that displaying a telescope wrong way up might be rather off-putting to a potential purchaser. The fellow insisted I was wrong; that the telescope was mounted correctly. I told him I owned one. He expressed surprise that I could see anything, since I was not using the telescope properly. Well, I wasn't going to waste any time arguing with him: someone else's ignorance is their problem - I've enough of my own. But the incident got me thinking: dumb bastards like that don't deserve my money - nor yours, if I can help it.

References