autocollimators (was Test Peice for 3D finishing)

Stuff about autocollimation, including info about using a polygon on
a rotary table.

http://www.primenet.com/~davoptro/poa.htm

basicly, you shoot a light out through a telescope, bounce it off a mirror,
and it comes back. If you carefully adjust the mirror, it ends up in
the same place it started from.

Now if you turn the mirror even a tiny amount, the return beam moves.

The process is incredibly sensitive. As part of my physics education we
had a class where we had to measure a number of different things, all to
various insane accuracies. One of the things we ended up with was the
speed of light.
Our set up consisted of a laser fired down a hallway. 80' or so away
was a mirror at a slight angle. The return beam hit a second mirror
parallel to the first, and so "walked" back and forth 4 times, then off
into a telescope.
The thing was insanely sensitive to vibration. We had to do the experiment
at 3am on a weekend to get the building "quiet" enough to not vibrate.
Then we had to sit quietly for a long time before we could take measurements.
The beam went crazy once when a truck drove by outside.

an ad for a commercial autocollimator

http://www.primenet.com/~davoptro/catD-638.htm


And, for what it's worth, last time I was in a laser shop they were
using a milling machine as an optical table.