Re: [ATM] On Axis Foucault

["David Harbour" <scarab2@cox.net>]

Thanks, John-

Dave


----- Original Message ----- 
From: "john sherman" <atm@mail.johnspics.com>
To: <atm@atmlist.net>
Sent: Wednesday, June 15, 2005 4:33 PM
Subject: Re: [ATM] On Axis Foucault


>
> Hi Mike, all,
>
> >For a given separation between source and return the total amount of
> >astigmatism is always going to be the same regardless of whether >they're
separated vertically or horizontally
>
> I agree. The point is that the tester-caused astigmatism is only
detectable in the horizontal setup (assuming the knife and slit are oriented
vertical, and separated horizontally/laterally). It is there, yes, but
invisible in the vertical setup.
>
> For example, you could have a mirror with known astigmatism, put it in a
Foucault tester, and rotate the mirror around. At some angles you can't
detect the astigmatism. The mirror appears to be a sphere.
>
> Right?
>
> John
>
>
>
>
>
>
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>


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