On Sat, 10 Apr 2004 20:43:54 -0400, Davoud wrote:

I got into a little argument today with an expert on telescopes and
just about everything to do with them (not a self-styled expert,
either, but a recognized expert). I showed him my drawings for a pier
that I'm going to have built.

My base mounts in the same manner as an AstroPier
http://www.astropier.com/installation.html, which means that it will
be mounted slightly above the concrete foundation by the use of hex
nuts on the J-bolts above and below the pier's base plate to allow for
precise leveling of the top surface to which my Milburn wedge will
mount.

The expert said that it is unnecessary to mount the pier in this
manner; it should bolt directly to the concrete footing for better
stability. He said that it does not matter whether the pier is exactly
perpendicular to the base; a couple of degrees in any direction will
not affect telescope tracking.

In general, I agree. The best pier is one that is set solidly in concrete. It
really doesn't matter if it is slightly cocked. You perch the pier up on bolts,
and you just increase the possibility of nasty resonant modes.


I argued that the base of the wedge (and, if shims are to be avoided,
the surface on which it mounts) must be as level as possible;
perpendicular to a line dropped from the bottom of the wedge to the
center of the Earth, if you will. I've always assumed that that is why
they put bubble levels on wedges.

Otherwise, I reason, as the telescope follows a fixed star, adjustments
in declination will be required as well as movement in R.A. The result
of that, I believe, would be slight field rotation over time.

In an equatorial configuration, all that matters is that the polar axis of the
scope is pointing at the pole. This is not determined by how level the bottom of
the wedge is, but by the position of the top of the wedge. The only reason to
have the bottom of the wedge level is so that the altitude and azimuth controls
used for polar alignment really are altitude and azimuth. If the base isn't
level, there will be some interaction between the two. But a few degrees out of
level is going to result in negligible interaction, and if you are permanently
mounted, it doesn't matter because you will only polar align once.

I have an LX200 mounted on a Superwedge, which is on top of a pier set in
concrete. I made no heroic efforts to make sure the pier is perpendicular to the
ground, or that the top of the pier is parallel to the ground. I'm sure it is
within a degree or two, that's all. My tracking and goto accuracy are superb.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com