[ATM] The 15.5 Ultrathin Project

[vorblesnak@peak.org]

I snapped a photo of the mirror with three hours of grinding on it.  It is
at ..

http://www.atmlist.net/contrib/vorblesnak-at-peak-dot-org/15%20inch%20ultra%20thin/Three%20Hours.jpg

Notice the artifacts at 3 o'clock, 6 o'clock, and 9 o'clock respectivly. 
These would have been high spots on the slumping mold so they are a bit
deeper.  After three hours I have reduced them by about 50%.  I am using a
blend of old grit from several sources.  It is mostly 220, with a bit of
120 and 320 in it.  Maybe some 400.  When I reduce the artifacts by
another 50% I will switch to clean 320 to finish the course grind.  Then
on to 500.

I wet the mirror down and did a basic reflection test for focal length. 
The ROC is roughly 150 inches, so the fl is about 75 inches.  Somewhere
close to an f5.  This is about what I calculated the focal length to be. 
I am getting a good match between the mirror and the tool.  Next time i
will do some shots of the tool and the mirror on top.

15.5 inch diameter
3/16ths inch thickness
f5 plate glass

David Davis
Toledo, Oregon 97391

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