From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


THe easiest way to test a convex sphere is with a thing with a fancy name
called a "test plate". In truth, the thing is nothing more than a
concave spherical surface that you match the convex sphere against.  As
long as you have about 50% of the diameter, you can do a decently good
comparison and expect decent results.  The optimum, of course is to have
the test plate at least as large or larger than the surface under test.  
The actual test is
the same as for a flat surface and the evaluation of the test is
essentially the same.  Curved surfaces will end up doing slightly different
things as the light is reflecting at different angles than that of a flat
surface but the difference is only valid when very tightly controlled
surfaces are desired.  For determining ROC and sphericity, the differences
are almost nil relative to a flat.
Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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