Re: [ATM] Help my 17.5 inch coulter mirror is astigmatic

["Carl Vehmeyer" <carlveh@wxs.nl>]

We tried to correct the problems with the mirror by starting at grit size
400. During in the process of grinding the mirror was placed on a wooden
board that's mounted on a barrel. The back of the mirror rests on carpet to
distribute the forces (we've made lots of mirrors this way, the all turned
out fine). I guess the problems arouse from the fact that we only turned the
mirror when we went from one grit size to the next. Polishing was done by a
machine which in hindsight is probably also a factor in creating renewed
astigmatism. So I guess I need to go back to grinding again.

Thanks for all the advise and support,

Carl


As Francis noted, not rotating the mirror during grinding is almost
guaranteed to produce astigmatism.  It looks like you will need to go
back to re grinding.  You probably only need to go back to 25 micron
unless the astigmatism is really bad.  Don't worry about the back in this
case unless there is a large amount of wedge in the blank but this is
unlikely.  Good luck with it.

Jarvis Krumbein

 
On Tue, 26 Feb 2008 14:01:38 -0500 "Francis J. O'Reilly"
<foreilly@verizon.net> writes:
> Carl,
> 
> Am I to understand that you did not turn the mirror at all during 
> grinding 
> and polishing?
> 
> If that is the case, astigmatism is a foregone conclusion
> 
> Please advise,
> 
> Francis J. O'Reilly
> ----- Original Message ----- 
> 
> 
> 
 

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