Well the 900 is an excellent match fro the 155 EDF with 4 " or standard
focuser. You do not need the 1200 ..it is VERY HEAVY. As to using a
tripod...I have never seen a 900 on a tripod..only the portable piers...I do
not belive you can use a tripod with the 900...and even if there was a way
to do it ...i do not recommend it. The 900 on the 48 portable pier is a
fantastic combo with a 155edf on it. I have one like this for my 155edf/f
(my 180edf is on my 1200) and YES it is a great combo and easy to
transport...TRUST ME the 1200 is VERY HEAVY!

I'll second Charles. To be precise, the 1200 is more than double the
weight of the 900. 80 lbs is a weight to be truly reckoned with if you
have to transport the mount long distances to dark sites.

I have an AP 155 EDF, 4" Field Flattener, and a Pentax 6x7 attached to the
end of it. And on top of that is an AP 80mm guidescope. The AP 900
carries that load with superb stability and tracking precision, even in a
moderate wind. Check out some results:

http://www.astrocruise.com/aln99.htm
http://www.astrocruise.com/m31.htm

I wouldn't try to use a tripod. With any kind of long tube you'll have
problems with it hitting the tripod legs. AP manufacture the Portable Pier
for a good reason - it is perfectly matched to GEM mounts, and the AP mount
in particular. It is very rigid - much more rigid than any tripod I have
used. The Portable Pier seems to really 'dig itself in' to the ground.
It's the closest thing I've seen to a permanent pier, and rock solid in
operation.

--Philip
Philip Perkins - philip@...
Wiltshire UK & Luberon France
Astrocruise - http://www.astrocruise.com