Re: Rayleigh Water Test (Was: Re: [ATM] 30" Flats)

[Mark Holm <mdholm@telerama.com>]

It has been noted by people trying the Raliegh test, that a very thin 
layer of water naturally damps out ripples better than a thick layer.

Also, you might want to buy a copy of "Best of ATM Journal" 
http://www.willbell.com  There was a rather long article describing how 
the author used just the setup you describe, only he was using it to 
test flats rather than the paraboloid.  In that setup, the paraboloid 
quality was not a big factor.  He was viewing interference fringes 
between the flat and water.

BTW, it isn't at all hard to calculate the error introduced by the fact 
that the water follows the Earth's curvature rather than actually being 
flat.  Just use the sagitta formula with the Earth's radius.

Mark Holm
mdholm@telerama.com

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