This post is brought on by seeing cheap little telescopes being advertised as offering 500X magnification and other such nonsense.

First off a telescope alone doesn't give any magnification. An eyepiece, working in concert with the telescope does that. A telescopes function is to gather more light than your eye can, and focus that to a spot where you can then utilize an eyepiece to magnify the image.

The amount of magnification achieved is calculated by the focal length of the telescope divided by the focal length of the given eyepiece. So with my 8inch SCT which has a focal length of 2000mm if I use a 10mm eyepiece we get 2000/10=200X. Pop in a 25mm eyepiece and 2000/25=80X. Now lets look at my 90mm refractor with the same 2 eyepieces. The refractor has a focal length of 600mm so 600/10=60X and 600/25=24X.

Now on to the point I made that the claims of 500X from a small telescope are nuts. Is 500X possible, yes. But it is not usable. A good rule of thumb is that the MAXIMUM usable magnification you can use is 50X per inch of aperture. And that is on the best, steadiest nights. Normal usage is more in the 30X per inch of aperture. So the best magnification I could realistically look at in my SCT is 8*50=400X. So these little cheapo department store telescopes with their 60mm of aperture which is about 2.5 inches would have a maximum usable magnification of 2.5*50=125X. And the eyepieces that come with these are usually crap as well so you won't even get that.

Trust me, don't waste your money, save up and buy a proper scope with some good eyepieces. You will be glad you did. While you're saving up, get a planisphere, learn the constellations, and do some scanning with binoculars.