Often when I go out for night observations with a group, one question always seems to comes my way while I am busy pointing a telescope at some object.
“What is the magnification of this telescope?”
Now the question is not an incorrect one to ask, but I have realized that most of the times the thought behind the question is wrong. Many of us associate a telescope with the word magnification. Many think that a good telescope is one which provides very good magnification. This is a misconception.
The most important function of a telescope is not magnification. It is an important aspect, but not one which determines the quality of a telescope. The highest priority is given to the aperture of a telescope. Aperture is the size of the primary lens or mirror. In general, bigger the aperture better the telescope.
Celestial objects are very far away from us. Very little light reaches us from these celestial objects at night. So our aim in building a telescope is to collect as much light as possible from these faint objects, hence the importance of aperture or the size of the mirror or lens that collects light.
Our eyes have a small pupil which lets light go through. Our eyes have evolved to see in normal daylight conditions. But when we go out under the night sky, our eyes are just too small. We need to collect a lot of light and since we cannot increase the size of our eye, we funnel the light using a telescope.
Once our telescope has collected enough light, we see it through an eyepiece. This is where magnification comes in. By changing the power of the eyepiece, various magnifications can be achieved for the same telescope. Even a small telescope can give high magnification if you put a powerful eyepiece on it, though this is of no use to us because it would have collected very little light and hence the image quality would not be good. Magnification is helpful only after the telescope has collected sufficient light, which is controlled by the aperture. Typically an aperture of 8-inch is considered good for amateur astronomy. So the next time you see a telescope, ask what is its aperture.
(Cartoon by Tyler Nordgren. Source: NOFS/NPOI)
Nikhil Pawar
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astronomy telescopes
May 13, 2012
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