Re: [ATM] Foucault

[Ken Lowther <hermit@outofoptions.org>]

Quoting David  Williams <dwilliams1128@earthlink.net>:

> Hello list
>
> To do the foucault test: what do I do first.  I've turned the light 
> on, now do I center the light between the knife and the light house?  
> My house is stationary.  Next I see the image of the mirror 
> iluminated evenly overal, and when I move the knife to the left from 
> the right the light dissappears at once..  This means that the knive 
> is at the Radius of Curvature--- Right?  But what zone is at the 
> radius of curvature?  Is it the whole thing?  Or just one part?

It is the "whole" thing if it is spherical.  But, you need to learn to 
move the
edge more slowly.  Trust me on this one.  "Once you get it, you won't forget
it"......

>
> Next,  I've heard that I need to use a mask with 6 parts hins 
> Sixtests;  but the foucault tester I have is so sensitive that I 
> haven't gotten used to it yet.  Does any one have advice on this?
>

It simply cannot be too sensitive.  Perhaps you mean 'unstable'.  Likely from
the comments above.


> Also I understand how to use a micrometer, but I wonder what it's 
> used for (to measure what compared to the R of C).  The spindle is 0 
> zero when it is out and the knife is even with the light house.  Then 
> as you move the knife back from the house and lengthen the R of C the 
> spindle contracts and is closer to 9.
>

Again, you need to 'see the shadows' first to  understand the test.  Go 
back to
the tester and  be patient.



Hermit, holed up in Youngstown, Ohio
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