Hi, all,

The input I got was very beneficial, so thanks to all! Sorry if I missed
anyone in the responses that I got so far.

First, Greg, I'm going to visit your writeup and grab any ideas I can get!
I'm sure there's a wealth of information there. I just have been so dogonned
tied up, I haven't got there yet. <g>

Dray, I'm not presently using my cookbook camera, but an ST-7. However, your
point is well taken, and I believe that a search for external vibration is in
order. Thanks for the reminder.

Blair, you make a very good point about polar alignment and PEC. Luckily, I
have a permanent mount and observatory, so I have my scope very well aligned.
So much so, in fact, that I seldom turn on the DEC correction when taking CCD
images. However.. this ties nicely in with very good points made by Frank and
Doc, I believe.

I believe that the weight distribution probably is more significant than I
had realized, Frank and Doc. My scope is well balanced, but I can see that
this is but a minor factor as relates to the weight distribution. Changing
the moment of inertia is something that I hadn't really thought about. This
being the case, as soon as the skies clear again.. if ever.. I'm going to do
three things:

1. Do some SERIOUS investigation of the RA worm/worm gear interaction and
alignment. This is the one place that is the weakest spot for the problem of
changing moment of inertia, it would seem.

2. Investigate various weight balance combinations. I know that I can get a
'balanced' scope with my two counterweight systems, with a large variety of
combinations of the weights above and below the ota.

3. I'm going to check into the difference between PEC training without the
camera on, and with it on. Like many, I have simply popped an eyepiece in,
done my PEC training, shifted and/or added weights, then put the camera on.
DUH! It hadn't occurred to me until now that what I should be doing is to
look at the drive and PEC *with* the camra on! I have an off axis guider
around here that I haven't used in quite some time. I'm going to put it on
and look at the PEC and other drive actions with and without the camera in
place! I have a feeling that things will look a lot different under the two
conditions. Maybe even to the point of showing me what I've been missing!!

If anyone has any other ideas on why so many of us fight egg shaped stars
while the few of us (you) get nice stars, I'd certainly like to have them.

It should go without saying, that egg shaped stars aren't the only thing
wrong with an image that has them. Obviously, the entire image has been
distorted in the same egg shaped pattern! Various software tricks can be
used to 'repair' the stars, but it doesn't correct the image as a whole. And
as someone on the list recently said, the old saw of 'garbage in, garbage
out' is very true!!

Once again, thanks to all. I'll get back with any good information that I
may find. By then, I should know if the new idea I have for making PEC
training much easier, will work. <G>

Bruce Johnston

<<
snip
> 2. The moment of inertia of the system has been reduced alot.
> Removing the heavy FMB allowed me to move the counterballance
> weights much nearer to the center of the system mass. This lower
> moment of inertia had reduced the load on the drive systems,
> making it easier and (I believe) faster to make corections -- maybe even
> reducing "overshoots".
> >


Snip

<< When guiding with the pictor 201 you MUST be well polar aligned as the
dec drift in the several seconds required for the autoguider to get an image
can produce oval stars. The same can be said for PEC training, it is a must
if the autoguider exposures reach several seconds in length. >>


Snip

<< I found one thing that may contribute to your problem. It is the coolant
pump. >>

Snip

<< I wrote a long song and dance some time ago about the techniques for
stabilizing imaging systems when doing astropics at prime focus of the
LX-200 when guiding is performed using a guidescope. >>


Bruce Johnston Computing
<http://members.aol.com/bjohns7764>
Internet home for "SuperFix" and "MegaFix" image processing software.
Personal page: <http://members.aol.com/ccdastro>

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