Hi nobby2 (Neil),
to exploring the prospect of mirror making ATMing.
No body has chimed in at this point so thought it might be of interest to you to see a very simple rig made from scraps of ply, a 133LPI Ronchi screen, a cheap LED torch (has multiple LED's, covered all except one), a small piece of green cellophane wrapper paper, (through which I pass the LED beam), a few screws etc.
Pics: side view, front view, and a shot of Ronchi taken of my 33"f4.1 mirror,(still a work in progress). Photo of R-gram taken by free hand held Canon Power Shot A1200 digital camera.
I will let others show their test rigs for Foucault,(will be much more sophisticated than my simplistic Ronchi rig).
Stephen.