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


Yes, the stars that are annular AND have no tail at focus are at the
on-axis point of the primary.  That needs to be put into the center of the
view by moving the primary.  Remember that the secondary does no optical
work, just provides a convient folding of the path of the light and, as
such, should be a perfect flat surface.
Depending upon how you do your alignment, the black center of the secondary
obstruction in the out of focus image may or may not be concentric to the
outer part of the ring.  That difference tho should be a very small
difference unless you have a very short FL scope. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

--- BBBS/NT v4.01 Flag-4