On Wed, 05 Oct 2005 08:01:13 -0500, don holly
wrote:

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

OOPS! You're right of course. Shows what happens when you can't keep
all your attention on one thing.
Eric


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