Bart,

I don't think it matters too much how far away your eye is. I think what's important is that you be viewing close to the level of the LED. If you can see the entire mirror lit up without the knife edge in front of the LED, and can see the shadow move across the entire mirror when you have the knife edge in front, I think you will be fine. Be comfortable, no need to scrape your eyeball...

If you use a camera it should be enough to hold the lens up close to the opening without actually touching it - there's some wiggle room. (Try setting to infinity and a longish zoom.)

I doubt you'll need a scope unless your mirror is very small (<6") and extra long radius - like say, 11ft.

Gary