Re: Orthagonality/alignment issues with dual scope setup


ebuehrens
 

Hi Mark,

It would be good to know how much misalignment you're seeing, but my
guess is that the issue is not with the mounting hardware, it's in the
C-14 - either you are seeing mirror flop (which would produce
inconsistent pointing errors depending on what part of the sky the
scope was pointing to - or (just as likely, I think) the optical and
mechanical axes of the C-14 are not aligned. All it takes for that to
happen is for the central pipe on which the moving primary slides to
be slightly out of alignment with the mechanical axis of the OTA. In
that instance the "wedge" you're chasing is actually in the scope.

My advice: determine whether the error is reproducible over all areas
of the sky, which would favor my hypothesis #2, and then either
machine some clearance in the bolt holes so the cradle can be moved
slightly side-to-side, or (my favorite) just live with it. If you get
it sorted out once, I guaranteee that it will go out of whack in the
future. There are just too many sources of mechanical error in the
C-14. Good scope and good value but IMHO the design and mechanicals
are overtaxed at this aperture.

good luck,

Eric
www.taconicobservatory.com

--- In ap-gto@..., "Mark Squicquero" <docsquic@...> wrote:

I mistakenly posted this in the AP-UG group.

Hi all,

I have a general question regarding my current setup:

Ap1200GTO, AP 160, C-14, Robin Casaday tandem mounting system,
Homeyer Cradle on the C-14.

I've just begun to refine this setup and have found that there are
slight alignment issues ie the two scopes don't exactly align on the
same target. When I calibrate the mount using the Ap 160, pointing is
superb. I shimmed the C-14 between the Homeyer Cradle and the
mounting plate and it improved the alignment somewhat. ( I figured
that the AP scope/rings/ Casaday plate were probably pretty accurate
so I focused on the C-14/custom SS plate/Homeyer system). The
shimming consisted of "raising" the back of the cradle. I also found
that I had to slightly shim more one side of both the front and back
of the cradle. As I mentioned the alignment is improved but not
perfect. If I move the scopes so that one is above the other on one
side of the mount, I can move the tandem arrangement in pure dec very
slightly to bring the C-14 to target. So it appears the necessary
correction is to diverge the back of the OTA's very slightly by
shimming one side of the C-14.

My question is, how do I accomplish this? The C-14 fits very snugly
in the cradle and there doesn't appear to be any room to shim. I've
tried loosening the mounting bolts and applying pressure to one side
of the cradle and then re-tightening to no avail. My guess is that
the custom SS mounting plate, although very sturdy and cool looking,
has some wedge in it. I've read nothing but praise for the Homeyer
cradle as far as its accuracy and rigidy (which is why I purchased
it), so I don't think that is the source. Any suggestions would be
appreciated. If shimming won't work maybe I can try a different
mounting plate.

Thanks,
Mark Squicquero

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