Re: [ATM] Faucault testing questions

[Mark Holm <mdholm@telerama.com>]

Vlad,

I have to admit I don't entirely follow your argument.  I do want to 
make an objection, even though I am not 100% sure what it is I am 
objecting to.  Your argument appears to come from geometric or ray 
optics.  It is very well demonstrated that diffraction effects play a 
large, perhaps even dominant, factor in making Foucault shadows.  For 
instance, see Nils Olof Carlin's discussion of optimum mask opening size 
at http://www.atmsite.org/contrib/Carlin/couder/

I learned something very valuable from Nils' page: that the shadows will 
appear in different ways in opposite mask openings.  I had thought that, 
either the zones went gray evenly, or that they both went gray from the 
side that the knife edge was cutting, or perhaps that they went gray in 
a way that depends on the local slope.  Nils shows that the dominant 
effect, for a reasonably smooth mirror, has one side darken from the 
center of the mask opening toward the edges while the opposite one 
darkens from the edges toward the center.  I don't know if ray optics 
predicts this, but I kind of doubt it.  Sure enough, when I went back to 
testing, I saw that Nils analysis is correct.  The shadows really do the 
strange thing that he calculated from diffraction theory.

-- 
Mark Holm
mdholm@telerama.com


_______________________________________________
ATM mailing list http://www.atmlist.net/