To Reflect or Refract: Which Telescope is Better?

We want to buy a telescope. If not today, then some day. There are two types of telescopes: refractor and reflector telescopes. Before learning about optics, those names probably wouldn't have told us all that much, but now we can make an educated guess about how each of these two telescopes work.

The reflector telescopes uses reflection and its optics are made up of mirrors. The refractor telescope uses refraction by a combination of lenses.

In general all telescopes do the same thing, focusing faint distant light into an enlarged, brighter image. A refractor telescope uses an objective lens and a reflector telescope a primary mirror to collect as much light as possible from a far-away object. The object lens or primary mirrors focuses all of that light in one position inside the telescope. The eyepiece lens then magnifies the image at that position

So why chose one telescope over another? It depends on the user's purpose. Lenses do something that mirrors do not, bending light of different wavelengths to slightly different degrees, which is why light passing through a prism separates the light into a rainbow of colors. When our refractor telescope is focused on red light, it won't be perfectly focused for something that is blue, blurring the image.

This effect becomes worse beyond visible light for light with very long wavelengths, or much shorter wavelengths if we want to create only one image instead of having several different refractor telescopes tuned to different wavelengths of light. To make an image with a broad spectrum of wavelengths we'd need a reflector telescope. This is what the Hubble Telescope is, for exactly that reason. Astronomers probing the origin of the universe maybe prefer reflector telescopes, but for the amateur astronomer gazing at the Moon, Mars, and Neptune, a refractor telescope will do just fine.