[ATM] Fused Silica 20" blank

[William Marriott <bmarriott@pacbell.net>]

Hello everyone!

So, I have comited myself to purchasing the 20" fused
silica blank, even though it is a bit different than
what I had thought.

For some reason it has been ground down .250" to
remove some surface imperfections that would not of
bothered me.
It also has a central hole that tapers from 22mm-44mm.

It will arrive on Thursday afternoon!

I have been playing around with PLOP, and have found
the following: 
Diameter: 508mm
thickness: 38mm
central hole: average at 30mm
central obstruction: 4.25"

With 27 points, and with variable angles, PLOP tells
me that:

RMS error = 5.68837e-07  P-V error = 3.80676e-06

Looking at Mark Holm's page at 

http://www.atmsite.org/contrib/Holm/Plop_optimized_cells/index.html

it seems to me to be very good, with RMS error off the
charts.

If I back up and do 18 pts with variable angles I get:

 RMS = 1.12946e-06      P-V = 7.13222e-06

Looking at the RMS value, it still looks like it is
pretty good.  PV seems to be too close to not good
enough, but it is noted that RMS should be used, not
PV.

Am I seeing  this correctly?

Thanks for the assistance in this matter.

Bill




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