On Mon, 03 Oct 2005 18:19:35 -0500, Richard J Kinch
wrote:


This won't work with a simple beam. The laser spot will inevitably be many
times the size of the motion of the spot you are trying to measure.

(snip)

True, barring exotic lasers and optics. Now having dismissed what
won't work ..... let's devise what might work. Same idea, Eric
.....optical leverage .... but without the laser. Tape a scale on
the distant wall. View the reflection of the scale in the mirror
using a powerful (spotting) scope, preferably one with a reticle.
The scope can be close to the mirror because it's focussed on the
distant scale via the mirror.

Your line of sight via the mirror will move 0.1" at range of 159
inches, as you noted. The distant scale will appear to move that
much when the mirror rotates. With a 20X scope, it will be as if
you are viewing the scale from a distance of about 8 inches. You can
easily discern 0.1" from that distance. At least I hope you can!

Your scale may need to be marked with lines .025" thick for clear
visibility in your scope -- depends on the scope. I can very easily
discern .025" lines at 100 feet thru my inexpensive spotting scope,
though it doesn't have a reticle. A good riflescope of 20X or more
magnification, or a transit or theodolite, would work well.