[ATM] The Ultra Thin 16 Inch Project

[vorblesnak@peak.org]

I took the completed uncoated mirror, mounted in a foam tube, to the
Oregon Star Party last weekend.  Star testing showed the importance of
collimation and the weakness of my tube design.  Still,  I was able to get
some pretty good tests in.  The image was about the same on both sides of
focus, a slight hairy edge inside, but I expected that.

The cell was a modified plop design.  The two outer rings of a 54 point
cell were used.  These were done in foam buttons glued to the cell, which
was curved to match the mirror.  The cell was made of wood and turned on
the bowl lathe.

After testing against Vega and Arcturus I brought M13 and M31 into the
scope.  Both resolved fairly well.  Poor detail but no distortion. 
Another observer who was there brought a nebula into the view and we could
both see some nebulosity.

I suspect the mirror is a bit under corrected yet.

While there I met the man who had slumped it and he said he remembered the
glass being 3/8ths not 1/4 inch.  I measured it when I got home and found
the edge to be right at 5/16ths.  Thicker than I thought.

I was asked how it was that the mirror kept such good contact with the
cell points and I said at the time I did not know, magic maybe?  After
some thought I suspect slumping the glass changes the center of gravity to
the back of the slump hump.  So even on edge it is falling backwards and
seating into the cell.

16 inch ultra thin
5/16ths thick slumped mirror
55.5 inch focal length
Approx f3.5

David Davis
Toledo, Or 97391

_______________________________________________
ATM mailing list http://www.atmlist.net/