Eric,

I think you forgot a factor of two again -- the spot should move 1.13
inches if the mirror rotates 1/10,000 of a revolution. No problem seeing
that with a 1.5 inch spot.

I like the spotting scope idea too -- tape a scale to the side of a
spotting scope which has a reticle and view the scale through the
rotating mirror, and you've got a cheap autoreflection alignment scope.
But to get a clear bright image with the scope, you need a good mirror
that is about the size of the scope objective. The laser method has
lower resolution but can use a much smaller mirror.

Don Holly




All I've had time for today is to make a quick measurement to a closer
target. At 75 feet the spot is 1.5". And I calculated that the spot
will move .568" at 75 feet. So, the spot is about 3 times as big as
the movement of .0001". But, the edge is pretty well defined, so I can
see the edges move. If I draw lines at the edges I'll be able to see
how much things have moved. I have a couple lenses that I used on a
laser pointer to get a smaller spot at 30 feet. They worked pretty
well. But laser pointer spots are not round and so any improvement
really helps. I was surprised how much the beam expanded. As for the
other ideas posted here, they have merit and if I can borrow a 20 or
so times scope these will be explored too. It sure is fun to learn new
stuff.
Thanks,
Eric