Makes an image using either a lens or a mirror, which magnifies an object that is far away for observation. The lens refracts light. The mirror reflects light. Bigger is better. A bigger area intercepts more light.
Area is proportional to the square of the diameter.
It is a lot lighter and the color effects are much truer. The purity gets worse as the lens gets bigger. Plus there are transmissive losses. Ground vs. Space. Information contained on this page does not represent the lecuture verbatim.