|  | To fully understand, you have to know a little about the nature of light, but don’t worry, it’s relatively easy, and very interesting. We use all sorts of measures for things in everyday life - beer is measured in pints, if you make a cake, you measure flour or sugar in grammes or ounces - and the measure for light is called the photon. Light travels around in photons, which are extremely small, so, to see an astronomical object clearly, you need to get as many photons as possible into your eye. Binoculars and telescopes are simply photon collectors – designed to collect as much light as possible, coming from a distant object, sometimes millions of light years away. There are two main types of astronomical telescopes, refractors, which collect light with an objective lens, as do binoculars, and reflectors, which use a mirror. Both kinds focus the collected light into an image, and then magnify the image through an eyepiece. Marvellous! Of course, the larger the objective lens or mirror in a telescope, the more efficient it is. If you decide to buy a telescope, I wouldn’t advise spending loads on any refractor with a lens of less than three inches in diameter, or a reflector with a mirror of less than four and a half to six inches in diameter – any less really doesn’t collect enough light for useful astronomy – much better to buy a good pair of binoculars in the meantime, and save like mad for something with a decent aperture. Beware of telescopes advertised by magnification only – "magnifies 400 times" may sound like the bees knees, but don’t forget there are only a limited amount of photons around at night! For decent observations, a magnification of x50 for each inch of objective lens or mirror is the limit in my humble opinion – any more, and your beautiful object becomes a faint smudge. So for a three inch refractor, no more than 3 x 50 = x150 magnification, and a six inch reflector, no more than 6 x 50 = x 300 magnificaton, and so on. This just means that the object is enlarged 150 or 300 times, compared to a naked eye view. If you go for binoculars, their power is described in much the same way as a telescope, by quoting the size of the objective (light collecting) lens, and the power of magnification in the eyepiece, e.g., 7 x 50 means a 50mm objective lens, and magnification of x7. I have a pair of this size and find them excellent – you could go for x10 magnification if you like, but any higher and you’ll have trouble holding them steady. Extra cost then looms in the shape of a suitable mount. You’ll definitely need a mount for your telescope – make sure it’s sturdy, especially if you want to try photography at some time. An image that moves is not a good one! |
