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

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

Thanks for replying to my call for help. The backside of the mirror is the
same as Don's mirror's (I guess "nubby" is the correct term). I've checked
for strain in the glass, there doesn't seem to be any. We've also ruled out
problems with the secondary and mirror cell by rotating the mirror during
startesting. The astigmatism rotates with the mirror so although I only have
a 9 point mirrorcell (calculated with Plop), the cell couldn't really be the
problem, or could it. Could the problem be that we didn't rotate the mirror
during grinding en polishing? Any thoughts on the "nubby" backside. Should I
grind this flat or is it possible to correct the astigmatism with slightly
less then perfect backside? If there isn't any strain in the glass, could
the glass still be inherently flawed. I presume it Pyrex, as far as I know
Coulter used pyrex in their 17.5 inch mirror's. 

 

Thanks again,

 

Carl Vehmeyer

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