Since I have a permanent setup I decided to use T point to do some
mapping and improve my pointing. I did mapping rung for the entire
sky. I got pretty good pointing accuracy on one side of the mount
(within 10 arcsecs) but when I would go to the other side of the
meridian the pointing accuracy would be several arcmins off the
target. I have been communicating with Patrick Wallace (the person
who wrote the T point program) and he used my model to try to make a
model that would have accurate pointing on both sides of the mount.
His model improved the pointing but I still had targets that were
almost on the crosshairs on one side of the meridian but would still
be off when crossing the meridian. Is this behavior that everyone
else is experiencing with Tpoint?

Also, if I park and then start up the next night, even though my
time is set very accurately, my pointing is off when I slew to a
star compared to how accurate the pointing was the night before. I
have also just trie powering the mount down without parking and
starting up from that poisition but still the pointing is several
arc mins off.

I am using the no beta ver of the keypad. I will also post there.

I had a similar problem using TPoint with my AP1200. In my case it
turned out that I was using the ASCOM AP driver in the Sky6 and it was
not effective in working with TPoint. When I turned to using the AP
driver built into Sky6, I saw dramatic improvements in pointing
accuracy when using TPoint. In fact my pointing errors across the sky
went down from many minutes to less than 15 arcsec (crossing meridian)

James

I few questions...

1) exactly how far off is it?
2) is it the same displacement no matter where you are on the other
side of the meridian?
3) When you go back to the good side of the meridian, are you still
pointing well?
4) Here is an important one - what method did you use to align?
5) I had similar problems. I lived with it for months. Finally, I
broke down and shimmed one end of my parallax rings with 4 thin
pieces of soda can and now I have no more pointing problems, with or
without a pointing corrector.
6) Which rings/mounting are you using? Does TPoint analysis describe
what is wrong? How much flexure is it reporting?

My thinking on my system was that, during a drift align, I could get
it smack on for a good hour long drift. However, if I went to
another part of the sky, it wasn't right. I'm not sure of the math
on this and I'm absolutely sure that someone will argue this point,
but my theory was that the mis-orthogonality was skewing my
alignment, this my pointing and tracking was messed up elsewhere in
the sky.

If you havn't already, I'd start looking at:
1) Orthogonality, since this is a one-time fix
2) Flexure - this plagues many owners of high-end mounts
3) Alignment - be sure that the "mount" is aligned, no matter what
the scope is telling you.

I suggest turning off TPoint pointing correction until you get these
3 resolved.

Good luck

Dave
2) Alignment

--- In ap-gto@..., "Barbara Harris" <barbharris1@...>
wrote:

Since I have a permanent setup I decided to use T point to do some
mapping and improve my pointing. I did mapping rung for the entire
sky. I got pretty good pointing accuracy on one side of the mount
(within 10 arcsecs) but when I would go to the other side of the
meridian the pointing accuracy would be several arcmins off the
target. I have been communicating with Patrick Wallace (the person
who wrote the T point program) and he used my model to try to make

a

model that would have accurate pointing on both sides of the

mount.

His model improved the pointing but I still had targets that were
almost on the crosshairs on one side of the meridian but would

still

be off when crossing the meridian. Is this behavior that everyone
else is experiencing with Tpoint?

Also, if I park and then start up the next night, even though my
time is set very accurately, my pointing is off when I slew to a
star compared to how accurate the pointing was the night before. I
have also just trie powering the mount down without parking and
starting up from that poisition but still the pointing is several
arc mins off.

I am using the no beta ver of the keypad. I will also post there.

At 12:36 AM 10/8/2006, mogulskier_groups wrote:

If you havn't already, I'd start looking at:
1) Orthogonality, since this is a one-time fix
2) Flexure - this plagues many owners of high-end mounts
3) Alignment - be sure that the "mount" is aligned, no matter what
the scope is telling you.

I suggest turning off TPoint pointing correction until you get these
3 resolved.

Dave: the whole point of using TPoint is that it fixes repeatable error.
It will guide you in getting polar aligned, and will compensate for non-orthogonality, etc.
There is no reason to "turn it off".

Dave

Yes, but in this case there is NON-repeatable error on top of the
uncorrected repeatable error. This is the crux of the problem. So, one
has to discover the source of the non-repeatable error and the best
way to do that in my opinion is to bite the bullet and manually get
rid of the repeatable errors first. Then one can try and figure out
what is really going wrong and the source of the non-repeatable
errors. This may not be the easiest method to use, nor is it the only
method to use, but it sure works a heck of a lot better than the
shotgun or guess and by golly approach in my mind.

At 03:50 PM 10/8/2006, Rick K wrote:

Yes, but in this case there is NON-repeatable error on top of the
uncorrected repeatable error. This is the crux of the problem. So, one
has to discover the source of the non-repeatable error and the best
way to do that in my opinion is to bite the bullet and manually get
rid of the repeatable errors first. Then one can try and figure out
what is really going wrong and the source of the non-repeatable
errors. This may not be the easiest method to use, nor is it the only
method to use, but it sure works a heck of a lot better than the
shotgun or guess and by golly approach in my mind.

Well, since non-orthogonality is corrected by TPoint you can skip that. Likewise, repeatable errors need not be corrected mechanically since TPoint will model them out.
You are under-estimating the difficulty in correcting non-orthogonality, etc. More power to you if you enjoy doing that though.

You need to look for loose parts that are shifting, things that flop, like mirrors or lenses loose in their cells, and if portable, assure that the pier is not shifting.

Dave