To: scottythefiddler ,
   Vladimir Galogaza , ATM shore

From: Tim Rickard 
Reply-To: Tim Rickard 




>   I don't know whether this curvature
>argument extends to most flats...i.e. I don't know what types of errors are
>prevalent on other flats.


I bought a quartz secondary that came with an interferogram. Although the
overall quality was very good, the edge was relatively low.  Looking at
only the 70% diameter in the report, the error looked like it was roughly
cut in half. This is good news, since as I understand it the typical well
sized secondary sees the on axis image only to about 70% diameter. I think
I've heard elsewhere that secondaries tend to have turned down edges.

I contacted the maker and suggested that he include the rms figure for the
70% diameter in his reports. He agreed that this would be reasonable (and
that errors are usually significantly reduced there) but he didn't want to
complicate the report further.

Tim

--- BBBS/NT v4.00 MP