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


I'll agree very strongly with the testing with a Couder Mask! Use a mask
for each zone rather than the multiple zones on a mask so that you have
absolutely no distractions from the other zones.  Also consider a dim light
in the room so that the white mask isn't dead black but rather a medium
gray and match that gray against the light coming back from the two holes. 
This will increase your ability to measure the difference between the two
sides of the zone.
You are wanting to make a spherical surface with a wavefront error of less
than 1/20th wave in order to be able to use that reference element to test
a good mirror.  You also want to know what those errors are so that you can
possibly be able to take them out of your measurements when measuring
1/40th wave optical surfaces that you may come across as you do your
figuring. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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