On Thu, 10 Jul 2003 23:50:49 GMT, William Hamblen ...reflected:

In article , Alan W Craft wrote:

Here is where I'd like to ask: Should the weight of the counter
equal or at least approximate the weight of whichever O.T.A. one
decides to mount? Will my 11 lb. O.T.A. require an 11 lb. counterweight
to balance it, or would the commonly-included 7-8 lb. counter suffice?
I understand that the counter may be slid up and down its shaft to
compensate, but would an exact match in weight between the counter
and O.T.A. be the ideal?

To balance you need m*d to equal M*D where m is the mass of the telescope
and d is the distance from the center of mass of the telescope to
the polar axis, and M is the mass of the counterweight and D is the
distance from the center of mass of the counterweight to the polar axis.
To minimize vibration you want d and D to be as small as possible.
Once you've bought your telescope d is fixed by the design of the mount
and you can vary D inversely with M. You also want to stay within the
weight capacity of the mount by minimizing m+M. The capacities quoted
by some manufacturers are optimistic. Sometimes it seems that they mean
the weight that just fails to collapse the mount.

I'd like to place a Parks 8-inch f4 "Nitelight" on a Vixen GP-DX, but thus
far the only place I've seen the weight of the Parks O.T.A. even remotely
specified is here...

http://www.astro-optics.suite.dk/supnew.htm

....but I believe that the Parks rotating-ring system is included in the 13 kg.
specification. I would, of course, use the non-rotating Vixen rings which
should weigh somewhat less. With the GP-DX load capacity rated at 10 kg.
I would defintely be pushing it, that is, if I incorporated Parks's rings which I
wouldn't.

Now off to hunt for the weight specification of ONLY the O.T.A.

Alan