there are two main types, all though there are five in total. the first one is called a refractor telescope, which uses a lense to bend the light into an eyepiece. these tend to fog up in winter time but give accurite pictures. a reflector telescope uses two mirors to reflect the light into the eyepiece. you can make these as big as you want and they dont fog up, but the immage can be distorted if the mirror angle is off by the slightest degree. of the two, i would say that the reflector is better than the refractor.there is a limmit to the size of the refractor.