Re: New member - advice on switching from G11 to AP900

Joe Zeglinski

Thanks Roy,

That helps. I see what you mean - if I back off on one AZ adjust knob
slightly, and move the mount indoors, I can repeat the reinstallation next
time, by carefully snuggling the mount back down, against the same original
adjuster side, and retighten. Just wish the mount had slots for the bolts,
which would mean less time trying to insert them. That should work.

Otherwise, I just need to have my own "900FSA" flat surface adapter machined
for me, with "drop-down-and-twist" bolt slots.
You bring out some good points.

Thanks, that is a relief.


----- Original Message -----
From: "roy" <roystarman@...>
To: <ap-gto@...>
Sent: Thursday, March 29, 2007 5:29 AM
Subject: RE: [ap-gto] New member - advice on switching from G11 to AP900

You can remove the AP900 mount form the pier by loosening 4 knobs. The pier
can remain and adapter plate can remain. The adapter plate doesn't have any
drilled through holes so they won't let stuff get down inside. I think you
should go to the AP site and download the manual for more details. You also
do not to have to full disassemble the mount for transport. I leave the Dec
housing attached and simply take off the counter weight and shaft. You may
loose your azimuth adjustment when doing this taking the mount off since you
have to loosen one of the screws. You can minimize that though by a marker
or some thing similar to mark the one screw and only loosen the other. When
you put the mount back together, use the mark to make sure you first screw
has not moved and then snug up the second to the azimuth adjustment block.
This should get you to back within a minute of where you took it apart. In
comparison to the G-11 it is indeed a Mercedes vs. a Chevrolet. An AP 900
in good running order will track within +/- 5 arc seconds and have a very
smooth periodic error. The bearing surface of the mount is larger and is
much less susceptible to a slight misbalance. With a TAK FSQ 106N My
periodic error is guided out and I rarely turn on PEC, but when I do it the
mount runs about 1.2 rms. I probably can't do better than that with the FSQ
as the scope for doing the polar alignment.. You will discover that you
polar alignment will be much better as the adjustments are easier and more
accurate than the G-11. I think the G-11 Semi-pier tripod is a great design
but the throat is too small for a 900 which is designed to use a 8 inch
pier. Perhaps you know someone who can make an adapter?


From: ap-gto@... [mailto:ap-gto@...] On Behalf Of
Sent: Wednesday, March 28, 2007 11:37 AM
To: ap-gto@...
Subject: [ap-gto] New member - advice on switching from G11 to AP900

Hello everyone,

As a new member, I am looking forward to scanning through more of
the posts in this forum, but in the short term, my decision time is
very short.

I recently acquired a used Losmandy G-11, and am on the learning,
but suddenly, well beyond my best expectations, an opportunity for an
AP900 GTO has come up, and wanted the advice from those of you who
have made the leap from a Losmandy G-11 Gemini to the Astro Physics
AP900 GTO. I suppose it might be like moving from perhaps the
Cadillac of computerized mounts - to the Rolles Royce. But before I
fully commit to a significant new expenditure, I would really be
oblidged to hear your own opinions, on the differences from using
your old G-11 and now your AP900.

For example:
One difference between the two that concerns me somewhat, is
switching the mount from the house, to a pier in the yard. With the G-
11, I can simply loosen 3 large aluminum pier knobs, and transfer the
entire mount to a field tripod - and back later. I wouldn't have to
redo any polar alignment, if I didn't readjust the polar elevation or
azimuth knobs. This saves a lot of time by skipping the COLD start,
and just doing a quick and simple WARM start.

However, looking at the "equivalent" AP900 take down items, it
doesn't seem quite as simple, just transfering from one pier
adapter "plate" to another. If I remove the RA assembly by detaching
the fork bolts (from the pier adapter), I no longer preserve the
azimuth adjustment. The other alternative is to remove the 6 screws
from the pier adapter "plate" itself, and then remove the (entire) RA
assembly, fork, and pier adapter, as a unit - this would be
to packing up the G-11 from it's tripod. The problem is that there
SIX of these smaller, black coloured, side-screws to handle in the
dark, which is just inviting Murphy to a star party!
The G-11 installation is so much easier - all you have to do is drop
the RA assembly into just 3 tripod slots, and give a quick turn
before tightening the 3 knobs - instead of searching for 6 screw
holes on the side, in the dark. Of course, I am talking about a
specific situation here rather than a permanent installation or a
full startup in the field.

You see my concern ... and that's just a handling issue, but what
the hopefully, MUCH improved performance of the AP900 over the pretty
good G-11? I would value your experienced opinions on that.

I still have some extensive reading of the AP900 manual to do, but
perhaps you could get me going.

Many thanks for any guidance, and reassurance.


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