I know this is kind of a noob question, one I should know the answer to by now, but what is the difference between a good lens and a crappy lens? I know that some lenses offer more zoom and wider apertures, but what else do better lenses have to offer, and why should I get one? Will it make my pictures look clearer? Better? I am deciding whether I should save up for a better lens for my D40 or stick with my 18-55mm kit lens.