| Blo*dy hell Jasp', I've just been looking at them this AM too. Chrimbo prezzie for No#2 daughter.
Guido will be able to help as the same knowledge for big lenses goes for telescopes. They are the same thing.
Magnification = Blimey snowy, I can see the pub from here. x100 is better than x50, simple really.
Resolution = Blimey snowy I can see the pub from here, and it's dead clear.
Focal length = bigger is better, but you drop the amount of light collected so, the bit where you see f5.6 or f16, etc, the smaller the number the better the light collection (brighter) the object will appear.
Long telescope is just that, it's long. Reflector is stubby and has a mirror in the bottom that reflects the light back up the body and into the eyepiece.
Bigger the reflector diameter the better magnification you get. Usual is 4, 6 and 8 inch.
Optics, the more accurately ground the less distortion and better imaging you get. High tolerances cost bucks, so you pay for what you get.
It's why Guido's 400mm APO f2.8 (is it?) costs 7 grand new, and my 400mm f5.6 cost 500 quid new. It's also the reason why Guido gets pin sharp pix and we don't apart from his shear talent.
Google to some of the telescope sites and it'll all be in there.
Ains.  | 
Jools
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