From: "Bill T." 
To: atm{at}shore.net
Reply-To: "Bill T." 


Jerry,

We've all been where you are now.

Rest up a few days.

Then press the optical "Reset" button by polishing that mirror
back towards a sphere with nice broad strokes and a big lap.  Don't rush,
don't put yourself on a schedule, just polish.  Star test frequently.  Keep
going until the 'stig is gone and the star test shows a nice round circle.

You probably got ahead of yourself on figuring, and wound up with a 'stiggy
mirror.   The truth is, you can't hand polish very long with sub-diameter
laps before 'stig sneaks up on you.  And it's almost impossible to
"figure away" 'stig with a small lap.  Such mirrors are very
confusing in the Foucault test, because every time you read it in a new
orientation, you think you're seeing the results of your last figuring
step.  Buyt what you're really seeing is just the effects of a different
amount of stig along a different axis.  You're readings are probably
accurate - it's just that you're correctly reading a different axis on a
stiggy mirror each time! Makes you crazy, nothing seems to make sense.

Start with a sphere and good edge, and be really systematic.  Star test all
the time, even when you're  far away from the final figure...it's a great
way to detect 'stig sneaking in.  Mark three different orientations on the
mirror about 45 degrees apart, labeled 1,2,3.  Take at least two readings
along each axis each time you do a Foucault test.  Make sure the readings
stay within a few percent.

You've learned a lot, you're almost there.

Bill T.




>From: "Jerry B. Hillman" 
>Reply-To: "Jerry B. Hillman" 
>To: 
>Subject: ATM star test
>Date: Fri, 30 May 2003 18:17:33 -0500
>
>
>Hi all,
>I had nice clear skies last night.  The boiling image I mentioned in my
>previous post was absent.  I modified my mirror cell sling and the
>triangular image dissappeared.  Outside of focus the image was round only
>in
>my imagination. Inside of focus the image was irregular and fuzzy. In focus
>the image was a irregular blob with no true form.  This was done at the
>maximum mag I can get to with a 3.6 mm eyepiece.
>Obviously, this mirror is junk, but more importantly, I totally mis-read
>the
>Foucault test. Maybe because this is a fast mirror (F4.5) it is more
>difficult? Maybe my eyesight is worse than I thought.
>I tried the wire test tonight.  Two passes produced readings that were so
>widely divergent that it renders the test useless to me.
>And since someone will ask - no, there is no one within 600 miles that is
>willing or able to help me.
>Dave Harbour tries to help me over the phone, but what I need is someone
>standing beside me.  I have belonged to an Astronomy club for over a year.
>The  guys there that have done a mirror are to busy with thier CCD cameras
>to help.
>Sorry for the negative air of this post. I am totally disgusted and
>discouraged. If I can't properly test it, then I might as well throw it
>against the nearest brick wall, haul the mount out to the trash and forget
>this.
>Jerry
>
>

_________________________________________________________________
MSN 8 with e-mail virus protection service: 2 months FREE*
http://join.msn.com/?page=features/virus

--- BBBS/NT v4.01 Flag-4