22-11-2008 Buying A Telescope (Article 164)

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Simon Kenny
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Joined: Tue Feb 12, 2008 9:17 pm
Location: Shannon, Co. Clare, Ireland

22-11-2008 Buying A Telescope (Article 164)

Post by Simon Kenny » Tue Dec 30, 2008 8:23 pm

Buying A Telescope (Article 164)
Many people ask what would be the best telescope for looking at the moon, planets and galaxies. We cannot recommend brands here but we can look at the aspects that make one telescope superior to another. The first thing we must stress is that magnification is probably one of the least important aspects in buying a telescope. What is crucially important is the aperture of the telescope; the aperture is the width of the telescope lens or main mirror, the width of the tube so to speak. The reason for its importance is that the bigger this is, then the sharper and brighter the images through the eyepiece will be. This is especially important if you want to use your telescope on faint objects such as star clusters and galaxies.
There are 3 basic types of telescopes, the refractor, the reflector and the SCT (Schmidt Cassegrain). Most telescopes with an aperture of less than 6 inches are refractors, telescopes larger than this are generally reflectors or SCTs. Refractor telescopes use lenses while the others use mirrors. A mirror is much cheaper at larger sizes.
If you see telescopes advertising very high magnifications, please keep in mind that these are theoretical magnification and might not perform at all well at such high powers. One thing worth mentioning is that eyepieces are interchangeable and they determine the magnification. In the telescope manual or written on a sticker on the scope will be something called the “focal length” expressed in millimetres. On nearly every eyepiece is a sticker with the eyepieces focal length, again expressed in millimetres. If you have a telescope with 1000mm focal length and an eyepiece of 10mm focal length, then the magnification produced is 100 times as it is the focal length of the telescope divided by the focal length of the eyepiece. Many astronomers have a set of eyepieces so they can view the sky at different magnifications.
Most telescopes that you might see in local shops are of the refractor variety, these are easily transportable and easy to set up. They have the disadvantage of having a small aperture. You might have to look further afield for larger telescopes. The key to getting a good price for a telescope is to shop around. The rapid take up of the internet by many people has revolutionized how people buy; the telescope market is no exception especially given the specialized nature of astronomical equipment.
There are several excellent astronomy shops in Ireland, Germany, England and the U.S. They have large websites where you can browse through the telescopes they have to offer. Make sure you look through several of these sites before you decide on the scope that is for you as prices can vary, do keep in mind that packages from the US will be subject to import tax and other levies.
If after looking through the websites you are still undecided on which telescope to purchase, the Shannonside Astronomy Club we can help you further at our monthly club meetings.

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