Johnsonian platforms

Does anyone have any experience with and/or opinions on the type V platforms?

Thank you!

Bennett

I've had one for nearly a year. I think they are
a good value for a dual-axis platform. I was using
a very light weight 8" scope on it (PortaBall 8"
around 32 pounds) and had alot of trouble with vibration
at first (at high power like 400x stars are elongated)
but eventually fixed it. Others with much heavier scopes
seem to feel there are no vibration problems.

After some thrashing around I was able to fix the
vibration with three things (1) silicon gel
pads between the platform and ground, and between
platform and scope. They are sold as Dr. Scholls
Gel Insoles or something like that at WalMart,
Giant, etc. (2) silicon plumbers grease on the
south bearing. The bearing is just aluminum running
on a teflon post, and I had a bad problem with
stiction. The motion was not smooth, but instead
many starts & stops per second. (3) I modified the
drive electronics to improve microstepping of
the motors. Items (1) and (2) alone are nearly
a complete fix, and but (3) helps also.

I have also used Tom O. platforms. My experience is
that they worked better "out of the box" but are
also significantly more expensive.

One comparative point: the Johnsonian is all metal,
so there is nothing to dampen vibration. Where as the
Tom O. is nearly all wood construction, which tends
to absorb vibration.

General comment: high-power observing is much, much
easier with a platform. The target will be in the
field center (best images) for many minutes with
the platform vs. few seconds without it. Planetary
details are much easier to see.