Re: [ATM] diagonal flat testing

[mdholm@telerama.com]

I'm thinking you want to be looking for astigmatism, because a slightly
spherical diagonal won't show much change in Foucault or Ronchi in the 45 degree
position, but will still produce astigmatism.

Use a pinhole source and look at the reflected image with a high power eyepiece.
 Rack the eyepiece in and out of focus.  If the image stays round both in and
outside of focus (roc) then stig is absent or at least pretty small.  If it goes
from a line or ellipse inside focus to a similar line or ellipse at 90 degrees
outside focus than astigmatism is present and may indicate curvature in the
diagonal.

Mark Holm
mdholm@telerama.com
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