From: "Jerry B. Hillman" 
To: 
Reply-To: "Jerry B. Hillman" 


Hi all,
When I tested my new telescope design for flexibility I put a laser
collimator in the focuser, collimated it with the tube assembly horizontal,
I then moved the tube to vertical while watching the red dot in the center
of my mirror.  It didn't move enough to measure.  I then tried the same
test with my 10" sonotube.  As I moved the tube towards vertical, the
laser dot started moving down.  At vertical, the laser dot was a full 1
1/2" below center.  Moving the tube back to horizontal returns the red
dot back to where it started. I know the focuser can't be moving. It is
bolted down. The secondary holder is reinforced with a plywood ring next to
the mounting points.  The mirror is secured and can't move, so that only
leaves flexure of the tube. Is this something I can fix, or is it just due
to using a cardboard tube. I am tempted to rebuild the 10" to match
the 16.5" I just built.
Also, couldn't this cause astigmatism? I have seen very slight astigmatism lately.
Clear skies, Jerry

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