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Re: [ATM] Flat grinding the back of the primary mirror

Vladimir Galogaza wrote:

>Stathis,
>
>So you made a finished mirror, found it astigmatic and then:
>
>
>>After grinding the
>>back flat and polishing for a while the astig disappeared.
>>
>
>Did you find out how & why does it work. What caused astigmatism?
>How do you grind back flat?  Using A,B,C method or else?
>How flat is flat in this case? Why polishing? How the astigmatism
>of the front surface mirror disappeared by working its back?
>
But, if the material was borofloat, one side was supposed to
already be quite flat (one of the advantages of float glass).
What happened to that side?
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