From: "Jerry B. Hillman" 
To: 
Reply-To: "Jerry B. Hillman" 


Hi everyone,
I have resolved my finacial problems and now am again working towards
finishing this 16.5" x 3/4" mirror. Progress update. I polished
the mirror back as close to a sphere as I could get it. As I am still
unable to work indoors, I only work on the mirror in the early morning or
late evening when the temperature is between 70 degrees and 85 degrees.
Today is a wonderful day. I have the day off and the temperature is an
amazing 70 degrees. Very unusual for August. I have been parabolizing with
a 7.75" star lap. The center solid part of the star is the same size
as my center zone, making it three inches.  I loaded Ronwin20 to my laptop
and have set it up next to my mirror so that I can do visual comparison
side by side.  Using this method, and altering the Conic value to -.75 I
found where my mirror matches the Ronchi pattern. I think this means that I
am 75% parabolized?? Please correct me if I am wrong. I am using a w stroke
with about 2" overhang.  The edge seems to be holding as the center
deepens.
I also took a critical look as my Foucault tester.  The numbers I have
posted in the past that showed the mirror to be at .9 Strehl or better were
invalidated by star testing. I wanted to figure out why. Careful study of
my tester and entire test setup showed backlash and slop in several of the
adjustments.
To remedy this I downloaded the plans for a tester from the Stellafane web
site and built a new tester and mirror stand from scratch. I mounted these
on a 16 foot 2x12 and set the entire assembly in my living room inclined at
a 20 degree angle. Initial testing shows that the tester is stable, moves
correctly on both axis, and has no backlash. I can control movement of the
stage in measurable increments of .001". I now have to learn to test
with a moving light source. This setup is much better than what I was
using. Time will tell if I can now get accurate measurements. As soon as I
get a web site up and working I will start posting Ronchigrams again so
that my progress can be evaluated by the list. I am glad to be back. I
missed you all. Clear skies, Jerry

--- BBBS/NT v4.01 Flag-5