Your guide to buying new telescope. Buying a telescope is a big step, especially if you’re not sure what all those terms – f/ratio, magnification, go-to – mean. So, to eliminate confusion and make sure you understand what you’re buying, here’s what to check out before you write the check out. Older, but very useful guide by Michael E. Bakich.
The 3 main types of telescopes use lenses, mirrors, or a combination of both.
Refracting telescopes use lenses – combining at least two, and as many as four, pieces of glass – as their objective (the primary light-gathering device).
Reflecting telescopes use mirrors to gather and focus light. In a Newtonian reflector – the most common type – light reflects from the primary mirror (whose surface is ground into a parabola so light comes to a common focus). The light strikes a smaller, flat secondary mirror near the top of the tube. The light then is bent 90° and enters the eyepiece through a small hole in the tube.
Catadioptric, or compound, telescopes incorporate a primary mirror coupled with a corrector lens placed at the front of the tube. The primary mirror’s curve is ground to a simple shape, usually a sphere. Ordinarily, a spherical mirror would introduce aberrations in the viewed image, but the corrector of a catadioptric scope “pre-bends” the light before it strikes the mirror. Two popular catadioptric telescopes are the Schmidt-Cassegrain and Maksutov-Cassegrain designs.
Further details in this interesting guide! Well worth your time!
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