Contrary to popular conception, the primary purpose of a telescope is not to magnify distant objects, but to gather more light than the human eye can on its own. In all designs this is achieved via a large (objective) lens or mirror which focuses the light onto an ocular or eyepiece lens in order to present the viewer with an image that is brighter, clearer and magnified compared to the eye alone.
Aperture is king
The aperture of a telescope is the diameter of the main lens or mirror, depending on the telescopes design. A telescope should not be judged based on claims of the magnification it can achieve and you should avoid like the plague any manufacture or brand who sells itself based on outrageous magnification claims (e.g. 300x or 500x etc…). These claims are usually a sign of a low quality product.
Key questions
When buying a new telescope, there are some critical questions that need to be answered to ensure you get a scope that enables you to see the things that interest and excite you as often as possible so you can get enjoy astronomy to its full.
1. What do you want to see?
Are you mainly interested in seeing the Moon, planets and other near Earth objects or more distant (and fainter) deep space objects such as galaxies and stars.
2. How often do you want to observe?
Smaller telescopes are easier to get out of the cupboard and setup and are faster to cool to the ambient temperature so the image stabilises. A smaller telescope you use more often is perhaps a better bet than a larger scope that requires planning and a group of friends to lug around.
3. Where are you located?
Are you in an urban area with lots of light pollution where you will need to travel to a darker spot or out in the wilds of the countryside where you just need to get the scope out in the garden. These factors, and your transport options will effect your choice of scope.
4. How much is your budget?
The telescope itself is only one aspect of the initial purchase. A good mount, eyepieces and potentially some filters depending on what you want to observe are essential and often overlooked as part of the initial budget. A good star chart and some astronomy books won’t go amiss for a beginner too.
Once you have answered these basic questions, it is time to start looking at the different telescope types available that best match the answers to the questions above.
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