Re: [ATM] data and musings on thin mirror

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

Dale posted a ronchi image of the 15.75" f/3.5 thin mirror here as the
ronchi challenge 2:

http://home.comcast.net/~doeason/rc/100lpi_outside_p150.jpg

Someone asked for more Ronchi images, so here's a simulated ronchi
test from the wavefront derived from Dale's interferometry of the
mirror, showing 20 longitudinal positions in 1mm increments (moving
source) through focus:

http://www.visi.com/~mkoehler/eason_davis_misc/davis_ronchi_sim.png

Dale's Ronchi image corresponds to the simulated images somewhere
between 7mm and 8mm outside focus.  For comparison, here is Dale's
perspective plot of the surface of the mirror derived from
interferometry.  However, remember that Dale subtracted the largest
aberration (spherical aberration) in making this image.

http://home.comcast.net/~doeason/DDavis/3_eights_3D_Surface.jpg

Theoretically, a lot of the mirror aberratons should be discernable in
the Ronchi sequence--even the primary astigmatism shows up pretty well
as a leaning of the lines through focus.  I'm curious whether anyone
can read the amount of spherical aberration from these images.  For
comparison, here's a simulation of a perfect mirror:

http://www.visi.com/~mkoehler/eason_davis_misc/davis_ronchi_ref.png

--
Steve Koehler
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