To: "Richard Schwartz" ,
From: Mark Suchting 
Reply-To: Mark Suchting 


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At 02:04 PM 31/03/2003 -0800, Richard Schwartz wrote: I am wondering if the
quality required in a diagonal depends on the distance from the diagonal to
the focal plane.   If the diagonal is very
close to the focal plane, perhaps error in the diagonal surface can't do
much damage....



Richard

Check the archives for  Anthony Stllman's recent excellent analysis of the
effect of curvature on the Newtonian flat  on the Strehl ratio using
Zeemax.

As many have known through practical experience, the flat doesn't have to
be nearly as good as popular literature suggests. No excuse for sloppyness
though. I guess the limiting factor of the  Diagonal focal plane distance
is the bottom of the focusser coming into the light path.

Mark







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At 02:04 PM 31/03/2003 -0800, Richard Schwartz wrote:
I am wondering if the quality required in a
diagonal depends on the distance from the diagonal to the focal
plane.   If the diagonal is very close to the focal
plane, perhaps error in the diagonal surface can't do much
damage....
 

Richard 
Check the archives for  Anthony Stllman's recent excellent
analysis of the effect of curvature on the Newtonian flat  on the
Strehl ratio using Zeemax.
As many have known through practical experience, the flat doesn't have to
be nearly as good as popular literature suggests. No excuse for sloppyness
though. I guess the limiting factor of the  Diagonal focal plane
distance is the bottom of the focusser coming into the light
path.
Mark





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