TELESCOPES and Things

When you tell someone you are an amateur astronomer, they quite often ask, "What sort of telescope have you got?" The answer of an f/10 12 inch Schmidt-Cassegrain will either send the questioner into a frenzied state of excitement, or total silence before they move on to the next subject.

The second question, if they get this far, is, "What is its magnification?" And this idea of magnifying images must be sorted out immediately, especially if you are thinking of buying a telescope.

The Magnification a telescope gives means NOTHING whatsoever. You should not even consider magnification when buying one.

This might sound odd, I mean surely you are buying a telescope in order to see things bigger. True, but any telescope that is worth buying will do that anyway. What you must start to do is worry when telescopes are using high-magnification as one of their selling points. E.g. small telescopes displaying "WITH A WHOPPING 200 TIMES MAGNIFICATION! - You're almost in Space!". In fairness, I am not saying these telescopes are uselss, but you will find them quite limiting, especially if you are a keen amateur.

Here is a basic guide to the size of a telescope together with its highest usable power:

Of course some rules are there to be broken, and I have happily used 300 times magnification on an 80mm telescope. However, what you get with over-magnification is a loss of brightness, contrast and detail. So, break these rules wisely.

There are some Minimum Requirements for a telescope: the 60mm example from the table above is really the smallest refractor you should buy. Anything smaller won't give you the astronomical brightness and quality you want. My first telescope was this size, and it really brought the night sky alive. On the reflecting telescope front, try to go for at least 100mm. However, I would seriously consider spending an extra amount to have a larger telescope which will last you much longer. The other alternative, of course, are binoculars, which give great views of the night sky.

What can I see with a Small Telescope?

Prepare to marvel at the craters & mountain ranges on the Moon. There are plenty of planets to observe (depending on the time of year): there's Jupiter and its four main moons, Saturn and its amazing rings, the dark-markings and polar ice caps of Mars, plus the changing moonlike appearances of Mercury and Venus. Comets, Asteroids, Double Stars, many Nebulae, Galaxies and Star clusters - All these, and a LOT MORE are all up there, waiting to be seen.

Let's just have a look at the different type of telescopes. There are three basic designs: the Refractor, the Reflector, and a mixture of the last two known as a Catadioptric type.

The Refractor is the well-known two-lens telescope. The big lens at the big end collects the light and focuses it down the tube. Here a smaller lens, the eyepiece, magnifies the image and throws it into your eye. Refractors tend to be more robust than reflectors and need much less maintenance. However, they are more expensive, size for size, and steady mountings are a problem in cheaper models.

The Reflector does just what it says on the box. A big curved mirror, at the bottom of the tube, collects the light and bounces it back up the tube. It meets another mirror which reflects the image out of the tube to a focus where the eyepiece takes over. Reflectors are cheaper than refractors as far as size is concerned. However, they don't care much for the odd bang though which can send mirrors out of alignment.

The Catadioptric type uses both lenses and mirrors to get the job done. The Schmidt-Cassegrain is one such telescope of this type. Catadioptrics are very portable, due to their compact design, but tend to be in the more-expensive price category as far as beginners are concerned.

Next we arrive at the Wibbly-Wobbly Factor. This is mainly the domain of the refractor, but can include some reflectors. It means, how stable is the telescope on the tripod? Some scopes are provided with little more than what I call the jelly mounting system. Without a steady tripod you will only have hours of entertainment watching planets, and the like, wobbling back and forth across your field of view.

Make sure the telescope you buy is mounted firmly. The tube must not shake if you are to observe successfully.

This is why it is a 'must' that you see the telescope before you buy it.

The best place to buy your telescope is from a recognised telescope or optical dealer. The telescopes will be built well and the staff will have knowledge of exactly what you want within the budget you have.

Happy Stargazing!