My physics teacher was saying the other day that in things like binoculars and telescopes, specially cut prisms are used to refract the light that enters them so that it has to travel further. He explained why but I didn't quite get it, can anyone here either explain it or link me to a page that would help me to understand why?

Not sure what he's saying about travelling further ...

I thought they used total internal reflection in the glass prisms as an alternative to mirrors.
Refraction is simply the bending of light. So, the light enters the telescope, bends in a funny way, and makes what you are looking at look a lot closer than it really is. It is the same concept when you look at something that is in water, and you are above water. That's why spear fishing is so hard, the fish isn't actually where you see it, but refraction makes it look that way.
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