ATM: 1st time Parabolizing Nightmare.

[Brand <huntb@ucs.orst.edu>]

Hello all,

I'm living a nightmare of frustration trying to parabolize my first 
mirror. It is supposed to be an 8" pyrex mirror with a radius of 
curvature: 109.75". A couple of weeks ago, I had finished polishing the 
mirror and proceeded parabolizing my mirror. Turns out that my pitch was 
too soft and I overcorrected about 8x.
After trying to bring it back to the normal paraboloid, I made it worse, 
about 12x. I gave up and went back to micron 12 and then micron 5 to 
bring it back to a sphere. I polished it again and started parabolizing 
last night. I did some tests and it seems that I overcorrected 
again. Bummer. Is it possible that I've been too sensitive on the tests? 
I've been using the Couder screen method and the "no-screen" method of 
just looking at the greyness (flatness).
My knife readings from the edge to the center should have a diff. of 
about .14", but it is around .4".
Does it matter how close my eye is to the knife blade during the Focault 
test? Do most people agree that it is easier to see shadow 
differences on mirror when tested in a room with a small amount of 
illumination as opposed to complete darkness? (I think Texereau wrote this.?)
I can't figure out how I parabolized the mirror so quick and then passed 
it. I test it every 2 minutes. The surface isn't just hollowed out in the 
center, it is a "good" hyperboloid (even though hyperboloid=bad in this 
case.)
If I use a far street light or a star as the light source for the test 
and then put my eye at the focus I should see the entire surface 
illuminated as in the Focoult as a sphere, correct? I'm going to try that 
now, see what it looks like, please tell me if I'm wasting my time.
What do the experianced do in a situation like so? Thanks.

__________________________________________________________________
Brand Hunt                 Email: huntb@ucs.orst.edu
Computer Consultant,       WWW  : http://www.engr.orst.edu/~huntbr
Information Services       Phone: (541) 737-9375

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