Foucault test limitations was [ATM] (no subject)

["Geoff Nelson" <gjnelson@absamail.co.za>]

Can anyone who has used the Foucault reduction program from 
sourceforge please comment on the ability of an image reduction 
system such as that to avoid this inherent problem with Foucault?

Geoff

From:           	Vladimir Sacek <vladis.2@juno.com>
Subject:        	[ATM] (no subject)
Date sent:      	Wed, 12 May 2004 14:31:54 -0400
To:             	atm@atmlist.net

> Nils,
> 
> >...but what if you don't get a tremedously accurate estimate of a
> >figure
> that is middling to lousy anyway?<
> 
> The problem is that it may be not even accurate, let alone
> "tremendously accurate". In making a mirror, no one starts out with
> perfect or near-perfect parabola to Foucault test. The test is there
> to guide you to as good parabola as it can be, and to have it
> confirmed in te end. If you don't know for sure where you are with the
> mirror at a given intermediate moment of transforming it from a sphere
> into parabola - or have wrong idea about it - how do you figure out
> the right way to proceed? Doesn't look like win-win situation. And
> such scenarios are exactly the source of frustrating inability to come
> to - or to confirm - even a decent parabola. 
> 
> I'm not suggesting that this is caused by test accuracy limitations
> alone. I merely point out that they are present. Errors resulting from
> setup/application/external factors are likely to be more of a problem.
> The test is simple in its principle, but the application can be
> tricky. Relatively small deviations/omissions from the proper
> setup/procedure, or unrecognized external factors, can easily make it
> a nightmare. Also, the Foucault is "designed" for nearly perfect conic
> figures; the rougher/wavier figure, the lower its accuracy. I think
> it's fair to say that really effective use of the test requires not
> only its proper setup/application, but also near-standardized
> parabolizing technic that keeps mirror's conical figure in a decent
> (or better) shape throughout the process.
> 
> Vlad
> 
> 


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