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Telescopes for the Amateur Astronomer

Apr 5, 2008
Binoculars with a strength of 7 X 35 can actually be a better choice than a telescope. Binoculars are more portable and convenient, relatively inexpensive, and it's wiser to get cheap binoculars over a cheap telescope. With the 7 X 35 binoculars, the first number stands for the eyepiece magnification and the second number is the aperture in millimeters. Binoculars of this caliber are lighter and easy to hold.

For those amateur astronomers, there are three types of telescopes available.

The most readily recognized type of telescope is the refractor, which has two lenses at the ends of its tube. It is important to avoid department store cheap models, as these quote large magnifications while having useless small apertures. Telescopes are made to collect light, not magnify images. Normal terrestrial telescopes have extra lenses to keep an image right side up, but this extra lense is left out of astronomical telescopes because it reduces light. Without a filter on the lens, rainbow tints can be seen around bright objects like planets. This is called chromatic aberration. Refractors can cost more than other types of telescopes, but, being smaller, these make great instruments for beginners.

The second type of telescope is the reflector. Light travels down a tube before reflecting off a couple of mirrors and through an eyepiece on the side of the tube. Reflectors need to be larger than a refractor to be equally useful. They do not suffer chromatic aberration, but the main mirror may occasionally need repolishing or realigning (collimating). There are kits available for this. Reflectors are often the most comfortable telescopes to use because of the eyepiece position. You don't have to kneel and possess an elastic neck to look straight upwards as you would with a reflector. A popular type of reflector is the Dobsonian, which has a mount near the ground rather than a tripod.

The final type of amateur telescope is the Schmidt-Cassegrain, and this uses lenses and mirrors to fold a light path back onto itself within a compacted tube. This telescope is usually less expensive than refractors, dearer than reflectors, and are easier to handle than both.

Sometimes telescope specifications quote numbers which will not affect the image you see. However, they can affect the exposure you need if you start into astrophotography. It is wise to get familiar with your telescope and the sky before you look into astrophotography though.

By joining a local astonomy club or checking a library, you can evaluate different types of instruments. Also, astronomy magazines have reviews as well as advertising for good telescopes.

Even though you should purchase the largest aperture you find, keep in mind you may not want a large telescope as you may have to carry it around. Smaller telescopes are easier to set up and use, and high pollution in your area can keep a large telescope from producing results to its full potential.

The best way to calculate the maximum practical magnification is to double the aperture number: i.e. a 60mm aperture shoudl yield a 120x magnification. You shouldn't waste time on buying telescope accessories, but should instead invest in the largest aperture you can find. However, don't be tempted to purchase an eyepiece that claims to stretch magnification beyond the calculated aperture value. Start off simple in terms of eyepieces. A Kellner eyepiece is a great general purpose piece, and if you place a Barlow lens between it and a focuser, magnification may be tripled.

In order to keep a moving object in view, a telescope may have to be moved repeatedly. To help with this, mounts and drives have been created. Electronic drives will help point the telescope, and it's important to have a sturdy mount.

It's important to know that many textbook and telescope advertisement photos are long exposures and have been given false colors. Since the eye isn't sensitive enough, stars will always look like small points of light and color will not be seen in dim objects.

Now, what will you be able to see with a novice telescope? With a 75mm refractor or 150mm reflector, you may see galaxies, nebulae, Saturn's rings, the large Jupiter moons, and countless craters on the moon. There are plenty celestial objects to help introduce you to the night sky.
About the Author
David Wildash posts information and resources on his website about Telescopes , and you can read more about buying a telescope
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