"A Telescope Buying Guide For Beginners"," It all depends on your astronomy goals and careers.
You have to look for the features you want in your telescope and select the best one's according to your requirement.
Refractor telescopes are long & thin, and known for their sharp, detailed and contrasty images.
If you are just a starter then a small, quality achromatic refractor of 60 to 90 mm aperture would be a good one.
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.
They are good for planetary as well as deep-sky viewing.
These telescopes collect light with a curved, concave mirror and with the help of their large apertures, they show fine, highly-resolved images.
Catadioptrics use both lenses and mirrors to collect and focus the incoming light.
Catadioptrics scopes are considered the most versatile telescopes and gives great all-around performance.
They show magnificent images of the moon, planets and faint deep-sky objects, when viewed in dark skies away from urban areas.
Compared to other two, these scopes have a wide range of accessories available.
Factors affecting the performance of a telescope
Aperture: Telescopes collect light from distant objects and focus it to produce images.
It is the aperture of scope (diameter of mirror or lens) that is responsible for gathering light.
Telescope Mounts: There are three basic mounts for telescopes altazimuth, Dobsonian, or equatorial.
It is mainly recommended for terrestrial viewing and casual stargazing.
It is a boxy altaz-type mount sitting close to the ground.
These mounts are more expensive and complicated than the altazimuth mounts.
Magnification: Magnification should never top the priority for buying a telescope.
Practically 300X is maximum magnification for good quality images.
Ideally there should have been three eyepieces for the magnification of a scope: one low, one medium and one high.
For observing the rings of Saturn, Jupiter, studying craters and valleys of the Moon's surface medium power of 80 - 100X are advised.
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