[ATM] Detecting Astig in Ronchi images

["Greg Jones" <gregj888@comcast.net>]

Dale,

It also depends on how bad the astigmatism is.  Some things to look for-
   1) tilt in the lines
   2) lack of symmetry in the lines.  
   3) I find it easier to see most shape errors (astif, zoning, holes) when the grating is scanned 
         across the mirror.  

I've been working on a 20" f/3.5 for several years (but not as much as I should).  The general 
test routine is to look at the Ronchi at ROC, inside and outside focus.  Then scan the surface to 
make sure I'm not digging holes or creating zones.  Last a Foucault test to see where I am 
and what to do next.   Note that I am using some small tools so have to be pretty careful.  
     
I find all the above tests tell you something the others don't or help in confirming the others.  


Greg Jones
http://home.comcast.net/~dac20/dac_001.htm
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