To: Scott Rychnovsky ,
 "Chris Feller" 
From: Mark Suchting 
Cc: atm{at}shore.net
Reply-To: Mark Suchting 


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At 08:34 AM 10/01/2003 -0800, Scott Rychnovsky wrote:


>  I find knife-edge measurements more useful than just saying that it
> nulls with a knife edge or that the Ronchi lines are straight: knife-edge
> measurements are quantitative.

But having visible errors on a reference surface defeats the purpose of a Null test.

If you have a `clean' sphere with no residual zones or asphericity, it is
easy to measure the height of the shadows on a parabaloid that is not quite
nulled and wave rate it without having to make allowances for an imperfect
reference surface.  Easier still, keep polishing.

~Mark



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At 08:34 AM 10/01/2003 -0800, Scott Rychnovsky wrote:

 I find knife-edge
measurements more useful than just saying that it nulls with a knife edge
or that the Ronchi lines are straight: knife-edge measurements are
quantitative.
But having visible errors on a reference surface defeats the purpose of a
Null test.
If you have a `clean' sphere with no residual zones or asphericity, it is
easy to measure the height of the shadows on a parabaloid that is not quite
nulled and wave rate it without having to make allowances for an imperfect
reference surface.  Easier still, keep
polishing.
~Mark

  

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