My Adventures with Foucault Testing

Tester

To evaluate the figure of the mirror I'm grinding, I decided to build a little tester. I took the basic design from Texereau and built a cheap and dirty version. Actually, I built 2 1/2 of them:

Mark I never saw the light of day
Mark II
Mark III

Screen

To do quantitative measurements one also needs a Couder screen or something similar.

Results

The hard part of all this is interpreting the results. Here are a bunch of Foucault shadowgrams of my mirror at various stages.

Other mirror testing WWW pages

Foucault tests:

The Foucault Test; the theory
Dwight Elvey's explanation of the geometry of Foucault testing
Victor P.'s tester
Chris Kovacs's tester and shadow sketches
Robert Duvall's tester and shadow images
Stockton Astronomical Society's Foucault test page and shadow images
Dave Kelly's very fancy tester
Berthold Hamburger's slit-less tester
Brad's slit-less tester

or buy one for $150 from University Optics
data reduction software for several platforms (including Macintosh!)

Ronchi & Caustic tests:

how to make a Ronchi screen
Mel Bartels' Ronchi tester
Mel Bartels' The Poor Man's Caustic Test

Bill Arnett; last updated: 1999 Mar 10