Re: [ATM] Stubborn Oblate Spheroid.. update

[Jason Hissong <jhissong@gmail.com>]

Bob,

Thanks for the information.  I am declaring this mirror completely 
polished out (it probably has been for at least a couple of 1 hour 
sessions).  I was expecting a complete void of any reflections from the 
laser.  Nothing appears that would make me suspect any left over pits. 

Here is the final ronchi diagram prior to figuring (another 45 mins of 
MOT, 1/3 diameter W strokes):

Inside ROC:
http://www.undermidnight.com/images/atm/sphere_2.jpg

Outside ROC:
http://www.undermidnight.com/images/atm/sphere_2_oroc.jpg

I was really trying for a perfect sphere... sigh.. oh well... I think I 
am pretty close.  The slight TDE bothers me somewhat, but being this is 
my first mirror to complete polish out, I am pleased with my results.  
This is an F4.3 mirror so figuring should be an adventure!  I still have 
a slight oblate sphere, but from the responses I have received, it is 
not a big deal.

The good news is that the scratch that I discovered early in polishing 
is completely gone!!!

Thanks for the help guys!

Clear Skies (unless you are working on a mirror)
Jason Hissong

Bob May wrote:

>The laser test doesn't end with absolutely no reflectioni of the
>light (a bare glass surface reflects about 4% of the light in the
>visible spectrum) but rather that when you scan the laser across
>the surface, you don't get any bright spots that are not
>reflecting the laser beam off of the generaly flat surface but
>rather at odd angles and providing a sort of specular reflec from
>the surface of the glass.
>When cldaning the surface of the glass, be sure to use paper
>towels that don't tend to shed fibers or you will end up with
>dust all over the surface when you wipe the glass.
>I'[ve gotten into the bad habit of suing the soft bottom of my
>forearms to do a quick wipe of the surface as this does a nice
>squeege action on the glass.  Wiping back and forth will make for
>all kinds of dust and leftover water so only swipe in one
>direction.
>Finally, if you suspect a pit, a quick swipe with your finger pad
>will show the difference.
>Bob May
>bobmay at nethere.com
>http: slash /nav.to slash bobmay
>http: slash /bobmay dot astronomy.net
>Addresses have been munged up to keep spammers from bothering me.
>replace the obvious words with the proper character.
>Thank you for your understanding!
>
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