Refractor: Uses convex lens to focus image at eyepiece
Chromatic Refractor: Uses a secondary lens behind the primary to better focus the individual colors.
APOChromatic Refractor: Uses two secondary lenses to get the best focus of individual colors. The Thomsen scope is APOChromatic, the most accurate type of refractor telescope. This type of scope becomes expensive and heavy.
Galilio’s telescope, through which he discovered the first four moons of Jupitor, was a refractor with a small (about 3″) lens.
Reflector: Uses a convex mirror to reflect light to a prism near the top of the scope which angles the light rays to the eyepiece. There are many variations of reflectors, and all large telescopes are reflectors (over about 40″) because a refracting lens becomes too large to maintain a consistent shape.
Frequently Used Astronomy Terms – Wikipedia Descriptions