Mark,
Are you using the CatsEye ³passive² collimating system: Sight tube,
Cheshire, and Auto-collimator tools? These are what you want to use to
really get great results not just using a laser beam collimator. In fact,
using only the laser collimator will still leave your scope with plenty of
collimation error.
Peter Natscher in Monterey
From: Mark Wagner <mark.wagner@No-Spam>
Reply-To: <mark.wagner@No-Spam>, The Astronomy Connection
<sf-bay-tac@No-Spam>
Date: Thu, 13 Mar 2008 15:15:39 -0800 (PST)
To: <sf-bay-tac@No-Spam>
Subject: [TAC] Collimation question!
I'm playing around with a CatsEye collimation system. I like this set of
tools, it has a nice
intuitive feel, and you come away with your gut telling you you've got it
right.
But I've noticed something odd, and think it may be not just this scope, or
tools, but an across
the board issue in Dobs with heavy mirrors. BTW... this is a 12.5" f/5 with
a 12 pound (I think)
conical mirror.
Using the laser (if you have a CatsEye, you know what I'm talking about)...
even just a plain old
single beam laser, when the scope is near horizontal, and I elevate it up to
say, 60 degrees, the
"spot" stays pretty much dead-on. But once I get close to vertical -
pointing to zenith - the dot
moves off dead-center.
Now, honestly, I recall this going on with my 18" Obsession too. And I
think my friends have
noticed the same thing.
I'm wondering the a mirror puts so much torque on the cell, that unless you
have a major beefy
cell in back with the glass glued to it, you're going to get some "shift"
when the scope is
pointed upward, and the stress is relieved?
The amount of shift is rather small, but it is there, I can see it.
Any comments, ideas, even rasberries? ;-)
Thanks,
Mark
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Received on Thu Mar 13 16:39:08 2008