From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


<<
Bob,
Great idea not tried using a 'grey' mask and matching to an external value
before - I must try that on my next mirror - down to the art shop for some
grey card I think
Many thanks
Francis
>>
Since I use a camera when looking at the mirror in the Foucault test, I
just have a light bulb in the room which produces a nice level of light on
the white cardboard that I'm using for masks.  It is the light level that
is desired, not necessarily the brightness of the mask itself. If I was
looking directly at the light past the KE then I would probably be desirous
of using a green color (I'm using a green LED on the tester) to balance the
color of the mask to the color of the light coming back. I will say that
the diffraction you get from an edge takes on a very interesting appearance
when doing this. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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