Re: [APML] Equatorial Mounts (other than an EQ6!)

["Joseph/Leslie Schaefer" <schaefer@htva.net>]

Hi Gene,
 If a system is stable for 60 minutes why wouldn't it be stable for 90
minutes? I would think the biggest problem
would be field rotation showing up with the longer exposures. With my 90
minute exposures I start to see some
field rotation at the corners of the FOV but the inner stars look fine. I
use a Tak FS-128 and guide scope.
 What kind of problems do you see with some of your longer exposures and do
you have any examples to show us?

Thanks, Joe Schaefer
www.starfillednights.com

----- Original Message -----
From: "Gene Horr" <genehorr@houston.rr.com>
To: <asdrich@yahoo.com>; "Discussion of Film Astrophotography"
<astro-photo@seds.org>
Sent: Thursday, February 20, 2003 2:54 PM
Subject: RE: [APML] Equatorial Mounts (other than an EQ6!)


> I'm going to rudely jump in here....
>
> > After several months of quietly lurking in the shadows of this group, I
> > had come to the tentative conclusion that an OAG is primarily a
> > tremendous pain in the telescope operator's tush.
>
> It is.
>
> > Not to put words in
> > your mouth, but your post would seem to imply that even though an OAG
> > can be challenging to use, once you master it, for imaging purposes it
> > is a superior configuration for imaging.
>
> It is.
>
> > ... Since I plan to use an OAG and manually guide for a while,
> > am I better off just sticking with the OAG and not using a guidescope
> > at all?  I have a moderate amount of experience with an OAG and
> > (forgive me) an LX-50, but I'm not sure how well the experience will
> > translate to the G-11/Tak 128 environment. Many thanks in advance for
> > your reply!
>
> With off axis guiding it eliminates quite a few sources of problems.
> So it is in one respect the superior choice.  But....for rigid OTAs
> (which a Tak 128 meets the definition of) and assuming a good
> guidescope and mounting it will work just as well for exposures
> under 1 hour (which my experience is limited to).  So for me the
> ease and flexibility of a guidescope outweighs the potential
> problems that can come even with a high end solution such as
> one of the OTAs not being securely fastened and slipping, either
> a camera or the autoguider shifting slightly in the focuser, etc.
>
> And even with high end instruments when you are moving to multi-
> hour exposures there are reports of slight movement.
>
> Gene Horr
> genehorr@houston.rr.com
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