Re: ATM Foucault tester

["Bob May" <bobmay@nethere.com>]

Jim, you really want to put the posts on the ATM list so everybody can reply
to the questions you have.
>>
Bob, I saw the photo of the tester and what struck me was the fact that the
LED light path didn't appear to be cut by the knife edge at all; it was a
fully round source...and big.  Does that have any bearing on the tester
working well?  My tester has the light hole being much smaller and the knife
edge cuts both the source and the reflection.  Seems like the larger the
source, the larger the focused image at the tester and it may be way bigger
than your pupil.
>>
First off, what tester?  If the photo of the tester is at an angle, you may
not be seeing the KE crossing the light source as the source is a bit behind
the KE and the angle of the photo "unmasks" the source.
The thing that is needed is a sharp decrease in the light level - I've
gotten shadows just from a naked LED that had a definite edge to the
reflection albeit that the edge, being round made for some apparent
astigmitism appear in the shadows.
The size of the light source is pretty much irrelevant as the actual light
that you do see is just from one point of the source.  A larger source
allows for your eye to move more vertically without losing the image of the
mirror's shadows more than anything else.
You may want to stop by my website and peruse through the article I have on
the Foucault Test.  It may make things clearer to you.  If you have any
questions on the subject, and relating to the article I'd love to hear them
as feedback always makes things better with me.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net