On Mon, 26 Dec 2005 01:56:18 -0500, Davoud wrote:

When I built my tiny zerbatory it was not in my mind to switch from a
fork mount to a German Equatorial Mount (GEM). Using my profound
knowledge of both plane and spherical geometry, which knowledge is
measured in truly irrational numbers on the Euclid scale, and relying
on information provided by Le Sueur, my pier manufacturer, I determined
that the pier needed to be approximately 15 cm (6 in.) due south of the
center of the dome. I hit the target it within a millimeter or so and
it has worked like a charm. Dome rotation is not automated, but that
did not present a problem; I could observe for quite some time or make
quite a number of DSLR images before I had to manually rotate the dome
a little bit to keep the target in sight of the finder, the Telrad, and
the 8" SCT.

Now, however, I am in the process of installing a GEM. A GEM ought to
be in the center of the dome, I am told. Moving he pier -- and the
1,600 lb. concrete footer it rests on -- is not an option. Rebuilding
the zerbatory around the pier is an option, but not one to be desired
or taken lightly. What kinds of problems, if any, am I likely to
encounter in tracking and fine guiding with the GEM improperly located?

TIA!

Davoud


I don't see why you think it would be an issue since you'll be there to
manually move the dome. If the dome was motorized, and under computer
control, it still wouldn't be an issue since all you would need to do is
define the dome/scope/mount geometry. This dome's controller could then
insure the slit would always be positioned in front of the scope's
aperture. But if the offset really bothers you, you could always install a
6" offset plate on top of the pier to center the mount.
-JATO
http://jatobservatory.org