I've noticed this with my Teleport. When I was shopping around for its
replacement one dob maker, who will remain anonymous, said there is a
similar shift with all dobs. My informant said it is not caused by pole
flexure, as I supposed, but by the secondary. Is your shift on the primary
or on the eyepiece target?
Andrew Pierce
-----Original Message-----
From: sf-bay-tac-bounces@No-Spam [mailto:sf-bay-tac-bounces@No-Spam] On
Behalf Of Mark Wagner
Sent: Thursday, March 13, 2008 5:02 PM
To: The Astronomy Connection
Subject: Re: [TAC] Collimation question!
Peter,
I'm using the BlacCat, the Infinity XL, and a barlowed laser with white
paper around the emitter.
Its a very cool system.
But still, that movement when approaching vertical is the real question....
Peter Natscher wrote:
>
> 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
> --
> GSSP Web Page updated 3/4/08: http://www.goldenstatestarparty.org
> Who's observing where? - http://observers.org/OI-calendar/
> Mailing list preferences: http://seds.org/mailman/listinfo/sf-bay-tac
>
>
> --
> GSSP Web Page updated 3/4/08: http://www.goldenstatestarparty.org
> Who's observing where? - http://observers.org/OI-calendar/
> Mailing list preferences: http://seds.org/mailman/listinfo/sf-bay-tac
>
--
GSSP Web Page updated 3/4/08: http://www.goldenstatestarparty.org
Who's observing where? - http://observers.org/OI-calendar/
Mailing list preferences: http://seds.org/mailman/listinfo/sf-bay-tac
--
GSSP Web Page updated 3/4/08: http://www.goldenstatestarparty.org
Who's observing where? - http://observers.org/OI-calendar/
Mailing list preferences: http://seds.org/mailman/listinfo/sf-bay-tac
Received on Thu Mar 13 17:22:31 2008