A Couder Screen
Here is a Couder screen for use with a Foucault tester.
Click on the image to get a large jpeg version or here for large gif version (same image, smaller file).
Load into your favorite image processing application, scale to fit your mirror, and print.
Then cut paste it onto a piece of cardboard and cut out the holes.
Measure the radii carefully (and enter the info in the table for reference if you like).
See Texereau section II-31 for details.
Here's an example of what it looks like with the knife adjusted for zone 1 (center):
and at zone 4 (edge):
Bill Arnett; last updated:
1999 Mar 1