Limerick Astronomy Club: Buying a telescope

Darren Barry

Reporter:

Darren Barry

Limerick Astronomy Club: Buying a telescope

Magnification is probably one of the least important aspects in buying a telescope

With Christmas just around the corner, many of you may be looking to purchase a telescope and one of the questions that we get asked the most is 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 three 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.

Most telescopes that you might see in local shops are of the refractor variety, these are easily transportable and easy to set up and so you might have to look further afield for larger telescopes. The key to getting a good price for a telescope is to shop around. Keep in mind that packages from the US will be subject to import tax and other levies.

Limerick Astronomy Club email: limerickastronomyclub @gmail.com