[ATM] Ultrathin mirror support study

[Dale Eason <atmpob@yahoo.com>]

I am using a mirror David Davis sent me.  It is
thicker than the one I used in the Ronchi quiz.  I
think it is 3/8 inch.  I'm not at home to measure it
and that part is not real important at the moment.  It
is coated and I was able to make good interferograms
from it.  

I put it in my 16 inch 18 point mirror cell and tilted
the cell back about 35 deg.  I took measurements
rotating the mirror every 22.5 deg.  I tried to only
rotating the mirror and not change how it laid on the
cell.  But that is very hard to do so sometimes I
changed the lateral forces on the back a little.

Lateral support is two pegs 90 deg apart that touch
the bottom edge. See

http://home.comcast.net/~doeason/16inchscope.html

You can see one of the lateral support bolts with a
nylon cylinder around it.

The original idea was to watch the figure rotate. 
What rotated must be on the mirror and what does not
must be test stand. Here is a movie that Steve Koehler
made of the results.

http://www.visi.com/~mkoehler/eason_davis_astig/anim.html

The box is 1/2 wave limit.  You can see that the astig
varies but does not correspond to the rotation very
much at all.  There are a few orientations where it is
almost gone.  However most of the time the edge is
highest where it contacts one of the pegs.  A few
times the astig is exactly vertical.

I think the bottom line is that for this configuration
it is very hard to control lateral support induced
astig.


Next we turned of the astig terms in the analysis. 
Here you can see the surface rotate as expected. 
There is still some variability at the edge but you
can see it rotate as well.  You can see a low edge
come up as it goes over a peg.  A high edge gets even
higher.

http://www.visi.com/~mkoehler/eason_davis/anim.html

I will be posting more analysis in the next few days
but I wanted to get this out becasue I think it is so
cool.


Dale Eason




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