Re: [ATM] Detecting Astig in Ronchi images

["Stephen Koehler" <s.c.koehler@gmail.com>]

Dale,

> If you can identify what it is that tells you.  Can
> you also estimate the major axis and/or the magnitude?

I can see the "leaning line" effect, but it is not nearly as
pronounced as in my simulation.  What grating did you use for this,
100 lpi or 50 lpi?

As in my simulations, if you look at the middle section of the center
line you can see that it leans a little to the left in frame 1.  In
frame 2 its lean is a little more pronounced.  The next two frames
take you through paraxial focus, and you can imagine that the lean
becomes extreme and "flips over" to the other side, although it's hard
to be sure.  By frame 5, the lean is to the right, and gets
progressively less in the following frames.

This lean of the lines as you go through focus is an indicator of
astigmatism that is not aligned vertically.  The effect is most
pronounced if the astigmatism is at a 45 degree angle.  I believe this
effect only shows up well when the surface is near spherical, as it is
in the middle 35-40% of this optic (notice the parallel lines in the
middle of frame 9).

--
Steve Koehler
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