[ATM] UltraThin tape as lateral support results

[Dale Eason <atmpob@yahoo.com>]

I put a strip of masking tape from the middle to the
top of the mirror.  The tape was longer than the
radius and the remaining was attached to the mirror
stand at the top.  So the tap was routed over the top
back pad.  The top back pad keeps the attach point
there.  Then the tape starts to pull away from the
mirror and angles to the top of the test stand.  That
keeps the mirror from sliding down the test stand
without the use of lateral support pegs.

What it does is remove all of the X astigmatism caused
by the pegs.  Following are three solid models of the
surface.  The first is with the lateral support pegs
at 30 deg.  It has the most induced astig.  

The white circles in the image are + and - .5 waves!
The 30deg pegs can generate more than 1 wave PV astig.
I have rotated the viewpoint conter clockwise from all
my previous post so that you can see the astig from
the side.  That is we are no longer looking from the
bottom front of the mirror.

http://home.comcast.net/~doeason/DDavis/pegs_30deg.jpg

Next the lateral support pegs are at 90 deg.  The X
astig is less.  You can see the mirror is folded less
and we are starting to see the 3 back support pads.

http://home.comcast.net/~doeason/DDavis/pegs_90.jpg

Now the haning from the tape with three back support
points.  The X astig is all gone.  Only that remaining
in the mirror as measured previously remains plus the
mess the 3 support point induce.

http://home.comcast.net/~doeason/DDavis/tape.jpg

So at this point we have learned that lateral support
pegs induce a lot of x astigmatism.  Best to try to
find some way to get rid of them.

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