From: Mark VandeWettering 
To: Scott Berfield 
CC: atm{at}shore.net
Reply-To: Mark VandeWettering 




Scott Berfield wrote:

> In the spirit of the list, I have avoided looking at the tester for
> several hours of polishing. I finally took a look and appear to have
> messed up. Can you folks take a look at the following links and give me
> some pointers on how to correct the sharp transition I am seeing? Am I
> totally screwed? I have been working tool on top with a W stroke of app.
> 1/3 total displacement. Mirror is 12.375" diameter, FL is app.
56", and
> the ronchi grating is 150 lpi. I have included a knife-edge image in
> case it helps.
>
>
>
>
>
> http://www.berfield.com/foucault5_11.jpg
>
> http://www.berfield.com/insideroc5_11.jpg
>
> http://www.berfield.com/outroc5_11.jpg



Take a deep breath.  You aren't screwed.  It looks worse than it is.

First off, I normally use 80 line screen for testing mirrors of this size.
I read the pictures you have as being a mostly spherical center, with a
fairly severe turned edge.   I'd probably continue with tool on top, but
just do center over center, and perhaps with a bit of a reduced stroke
length.  You've probably got a few more hours to go before you are really
polished out, so don't panic.  Test every hour to see if you are making
progress.

        Mark


>

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