Re: ATM Re: Dwight's tester

["Dave McCarter" <dmccarter@sympatico.ca>]

I guess the amount of light needed by a foucault source depends upon your
testing environment more than anything else. I use a two bladed slit about
50u in width and the green LED, I wanted to be testing at _my_ peak of
sensitivity, has been sanded flat with some 220 grit and gives very nice
even illumination of the slit. I think that is probably the most important
criteria, even illumination. Very probably also true for slitless single
edge testers.

I also have a high brightness Red LED off to one side of my tester, and a
small white target equally spaced on the other side of the knife edge. While
setting up the test I can see the reflected red light, and if I adjust the
mirror stand so that it hits the target then the slit image is at the knife
edge. Really speeds up testing!

Maybe when I rebuild the ronchi tester I'll get a blue LED.

Dave