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

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

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

--- Mel Bartels <mbartels@bbastrodesigns.com> wrote:
> > OK.  Since we had the round robin are we still
> focusing on 'larger' 
> > optics?  Any of those owners or observers care to
> report on the difference 
> > between star testing and Foucault testing?  Does
> this theory of under 
> > correction come with a number?
> 
> I've not been plagued with Foucault issues, but I've
> observed others who 
> have had consistent trouble.  I've always lazily
> ascribed psychological 
> reasons, but perhaps there is a physical basis. 
> That's what's being debated 
> now: Is there a physical basis that might be an
> explanation?  Don't forget 
> the entire gamut such as mirror cooling on testing
> stands, mirror 
> deformation on testing stands, biases on how the
> test is applied, et al.  If 
> a physical basis is found, it still remains to be
> demonstrated that it is 
> the cause, as do psychological reasons.
> 
> Mel Bartels 
> 
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> ATM mailing list http://www.atmlist.net/
> 

Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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