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


The KE blocks half of the lens with the edge itself in the middle of the
lens for best results.  This puts the beam passing by the KE in the middle
of the lens where the blockage from the aperture of the lens is minimum. If
the lens is stopped down too far (the F-Stop is too high) then the light
from the mirror surface will be attenuated and that will give wrong
results. If the edges of the mirror aren't at the same brightness as the
center of the mirror, any offset of the mirror in the image will make the
gray of the test be off from what it should be. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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