Re: [ATM] Re: [atm_free] The zonal Foucault test is free ofinherentcorrection bias - some supporting graphs

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Guy Brandenburg wrote:

> I am currently browsing a newly-acquired copy of John
> Strong's book on laboratory physical techniques
> (formerly out of print but available from Lindsay
> Books as a reprint). He points out that Foucault tests
> are sensitive to parallax, and has a method of working
> around that by using a half-silvered mirror so that
> the examiner's eye and the ray of light coming out
> towards the mirror are in exactly the same spot.
> I know that I always have about an inch or two of
> parallax when I use a Couder mask.
>
> Guy

I had always heard that one of the difficulties here was the aberration
introduced in the transmission through.  That was reduced by using
a pellicle (sp?).
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