Re: ATM Foucault test accuracy

["Steve Lindberg" <lindbergs1@home.com>]

   It has been my experience that amateurs tend to make overcorrected
mirrors and mass produced mirrors made by commercial outfits are
undercorrected, sometimes by a wide margin. My observation.
   I like to judge the shadows when they just begin to darken in the Couder
windows. I think Texereau recommends that, too.  I have often wondered if I
have a systematic error in my observations when performing the Foucault
test.  I think it is likely so. I can take a series of measurements and come
up with close to the same numbers each time, but who knows if they are
skewed by a repeating error on my part?  Someday I will pay to have an
interferogram done on one of my better mirrors to help calibrate my eyeball.
Besides the money issue, I a little reluctant to find out the truth. It
might hurt.
   It would be fun to participate in a Test-a-Thon, passing a mirror of
known quality around to see how our testing abilities stack up.  Anybody
else interested?  Those who want to participate would have to chip in to
have an interferogram made.
Steve Lindberg, Olympia, WA