Telescope | Eyepieces

Buying a telescope is a daunting task for a newcomer. It all depends on your astronomy goals and careers. There is no perfect one which suits all observers in all conditions. You have to look for the features you want in your telescope and select the best one's according to your requirement.

Selecting the proper type

• The refractor type telescopes best suit for watching moon and major planets. Refractor telescopes are long & thin, and known for their sharp, detailed and contrasty images. They collect light through multi-element lenses. If you are just a starter then a small, quality achromatic refractor of 60 to 90 mm aperture would be a good one. The best thing about a refractor telescope is that they are inexpensive, portable and almost maintenance free. A refractor telescope is also useful when you will be mostly observing from city or the surrounding areas where the night skies are lightly polluted.

• Reflector telescopes are also known as Newtonian telescopes. They are good for planetary as well as deep-sky viewing. However Newtonian telescopes are more fragile and need more maintenance than others. These telescopes collect light with a curved, concave mirror and with the help of their large apertures, they show fine,
highly-resolved images. The reflector scopes are not suitable for terrestrial viewing because they produce an upside-down image.

• Catadioptrics use both lenses and mirrors to collect and focus the incoming light. They are also called compound telescopes. Catadioptrics scopes are considered the most versatile telescopes and gives great all-around performance. They use a large aperture in very compact tubes. They show magnificent images of the moon, planets and faint deep-sky objects, when viewed in dark skies away from urban areas. These scopes are best suited for astrophotography. Compared to other two, these scopes have a wide range of accessories available. They can be entirely computer controlled.

Factors affecting the performance of a telescope

• Aperture: Telescopes collect light from distant objects and focus it to produce images. The light collecting capacity of a telescope is the most important feature. It is the aperture of scope (diameter of mirror or lens) that is responsible for gathering light. Larger the aperture, the more light gathered, the more you'll see.

• Telescope Mounts: There are three basic mounts for telescopes altazimuth, Dobsonian, or equatorial. Altazimuth is the simplest type of mount, providing up-down, left-right motions. It is mainly recommended for terrestrial viewing and casual stargazing. The Dobsonian mount was basically designed for easy maneuvering of large reflectors of more than six inches. It is a boxy altaz-type mount sitting close to the ground. Equatorial mounts are designed for the purpose of astronomical viewing. These mounts are more expensive and complicated than the altazimuth mounts. With the help of these type of mounts users can track or follow the motion of celestial objects through the sky with a single manual hand control.

• Magnification: Magnification should never top the priority for buying a telescope. The quality if image degrades with magnification. Practically 300X is maximum magnification for good quality images. Telescope's magnification is also known as its power and it is adjusted by changing eyepieces. Ideally there should have been three eyepieces for the magnification of a scope: one low, one medium and one high. Lower powers of 30 - 50X are recommended for observing galaxies, star clusters and nebulae as they are spread over a wide area of sky. For observing the rings of Saturn, Jupiter, studying craters and valleys of the Moon's surface medium power of 80 - 100X are advised. Higher powers of 150 - 200X allow the astronomers to observe mountain peaks and fine lunar detail, the surface features of Mars.

By Mike Kirsten
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