Reddit reviews All about telescopes (Popular optics library ; no. 9094)

Oh god, this question is such a can of worms that I will try to answer as best as I can. I'm not a master optician, a master optician will give you a different answer, you ask two master opticians and they'll fight about the answer, ask three and you'll never get a conclusion. I will try to answer this and break it into chunks. For simplicity I will talk about reflector telescopes, or scopes that reflect light back into the eyepiece, and not refractors which would be more like a camera lens.

Telescopes can be broken down into their individual aperture and F ratio, which is nothing like an f ratio in a camera.

Aperture controls the amount of light gathering a telescope can do and in some cases the contrast of a scope. Aperture it is literally the size of the primary mirror or element in the scope. A 10" scope would have a primary mirror 10" across and give light accordingly. The size of the mirror SHOULD have a play on the desired F ratio of the mirror which we'll talk about next.

Your F ratio for a telescope calculates field of view, which is directly related to your magnification. A small F ratio means wider fields of view, a large F ratio has a smaller field of view. F ratio also, to an extent controls brightness of your object, so, the more magnification the dimmer an object becomes, which means you want to make up for the dimness with larger primary mirrors.

Now we're going to get complicated, and I'm going to keep it simple. When you start with ridiculous amounts of magnification (provided by mostly by an eyepiece, but in some parts by a mirror) you end up with very visible defects, the most common is what we call chromatic aberration. It is a prism like shifting of colors in the objects you are looking at. Chromatic aberration comes from small defects in the mirror surface, perhaps an atom or two of silica in height, maybe three or four. (Yes, a good mirror is THAT precise) These color shifts can significantly impact your viewing of things like Alberio, Saturn, and well, just about any other interesting thing you could possibly look at. Other defects we worry about are things like astigmatism, which creates a conical star as opposed to a circular one.

So, simply put what you're getting for 3k+ is a finely figured mirror (that's what we use to describe the process of polishing a mirror to perfection) that has no optical flaws which will produce a smooth and apparition free viewing surface across the entirety of your field of view.

If you have more interest check out the following:
Alberio: http://www.albireovineyards.com/uploads/1/3/0/2/13028271/2582976_orig.jpg
Saturn Through a (pay attention especially to contrast and DETAIL):
Cheap Scope:
http://i1.ytimg.com/vi/9VIhag8tTcs/maxresdefault.jpg
Pricey Scope:
http://astrobob.areavoices.com/astrobob/images/thumbnail/SaturnJimSchaff.jpg
Scope that could have been a car.
http://www.learn.usa.canon.com/app/media/images/articles/60da_astrophoto/08_saturn__hero.jpg

For the hobbyists and clubbers among you:
www.stellafane.org
www.atmob.org

And for the technical readers a nice intro book on building your own:
http://www.amazon.com/about-telescopes-Popular-optics-library/dp/B0006CL970/ref=sr_1_1?ie=UTF8&qid=1404270285&sr=8-1&keywords=sam+brown+telescope