Re: [ATM] Milligan interferometry report

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Steve,

hope you have a great journey!

> The thing that struck me most was the test stand astigmatism issue.  I
> have often wondered how it would affect measurments.
>
> It appears that it manifested itself by causing the left and right
> edges of the mirror to bend away from the tester, effectively yielding
> the appearance of more correction across the horizontal axis, across
> which Foucault testing is typically done.
>
> This might tend to cause a person using the Foucault test with a
> Couder mask to believe the mirror is more corrected that it really is,
> if the test stand bends the mirror in the way it did in the report.
>
> That would tend to cause a mirror maker using Foucault to undercorrect
> mirrors.  Seems like someone raised a question a while back about why
> Foucault testing was producing undercorrected mirrors when compared to
> interferometry..... maybe this is why.

In principle I would agree, but I suspect the effects are too small to
matter much. It means that the difference in f.l. depending on diameter
tested would be something like a few tens of microns - far below the
accuracy anyway of measuring the paraxial ROC.



Nils Olof

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