From: "Jim Miller" 
To: "Mark Holm" ,
        ,
        
Reply-To: "Jim Miller" 


atmj had an excellent article on using water for flat testing just before
publication ceased. light source was a newt in reverse.

jtm

----- Original Message -----
From: "Mark Holm" 
To: ; 
Sent: Tuesday, March 11, 2003 5:55 PM Subject: Re: ATM flats



People have used a water surface as a reference for figuring flats.  I have
never tried it, so can't pass on any personal wisdom.  I think I read a
fairly
lengthy account in S&T quite some years ago.

Can't get much cheaper than water.  Of course water isn't really flat, it has
the curvature of the Earth.  That turns out to be small enough for most
purposes.  As I recall, you need to make a Fizeau interferometer setup, but
you
really should have one for testing glass flats against each other anyhow, so it
isn't really extra work.  Also, judging from what I have seen and read, it isn't
really very hard.

Biggest problem with the water flat as I recall is vibration.  You will probably
need to work on a concrete floor directly on the ground, like a basement.

Mark Holm
mdholm{at}telerama.com

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