Slew, Sync and Frame - Am I doing something wrong?

[chris_g]

Ok, what's wrong here or what am I not understanding. After I polar align, I'm using NINA TPPA because I can't see Polaris, I then do a star alignment on Altair with SynScan, then slew to Aldebaran, plate solve and sync then slew to Aldebaran again, Aldebaran is not centered in the FOV. I center Aldebaran in the field of view, plate solve and sync again, Stellarium is no longer pointing at Aldebaran. It's close but not quite there. Below are shots of the process. The targets are always up and to the right in the image, not that up and right mean anything in celestial coordinates. I'm always imaging to the east and north east since west and south west are toast to me. What I can't account for is when I center the target then sync the mount again the view shifts in Stellarium. It doesn't matter what database I use to slew to the target initially, the results are the same, so that tells me it's not Stellarium or SynScan.

I get good results with long exposure and guiding. If I haven't I've found the reason else where. So is this normal and there something I am not understanding about the coordinate system being used or is there something wrong with my polar alignment or perhaps something else? Thoughts, comments, and laughs at the newbie, all are welcome!

Slew to Aldebaran in Stellarium

APT Image after slew

APT Image after framing Aldebaran in center of FOV

Stellarium telescope position after framing

[Graeme1858]

Hello Chris

Just a thought, I haven't got APT on this machine. Are you using RA/Dec J2000 in Stellarium and RA/Dec On Date in APT (or vice versa).

Also, once you have your target plate solved what is the reason for re-slewing to it?

Regards

Graeme

[bobharmony]

+1 for the possible different coordinate systems. APT uses J2000, but will convert data it sends to planetarium programs to JNow. The button that controls the function is located on the "Gear" tab and is labelled "JNow". If it is selected, it will do the conversion, if not selected it will send J200 coordinates to the other program.

I use Cartes du Ciel as the planetarium program. I was able to get APT and CdC to play nicely together by setting CdC to use J2000 and by deselecting the "JNow" button in APT.

Hope this helps more than it confuses!

Bob

[chris_g]

+1 for the possible different coordinate systems. APT uses J2000, but will convert data it sends to planetarium programs to JNow. The button that controls the function is located on the "Gear" tab and is labelled "JNow". If it is selected, it will do the conversion, if not selected it will send J200 coordinates to the other program.

I use Cartes du Ciel as the planetarium program. I was able to get APT and CdC to play nicely together by setting CdC to use J2000 and by deselecting the "JNow" button in APT.

Hope this helps more than it confuses!

Bob

Yes it did help.

I plate solve using ASTAP in APT and ASPS stand alone for blind solve. Stellarium's telescope plugin, ASPS, and APT are all set to J2000. After some research, thanks to your nudge, I believe I understand what's happening. Everything should be using JNow since J2000 are the RA/Dec coordinates in the year 2000 and if I synced to that it would explain what I'm seeing.

Thank you.

[chris_g]

Hello Chris

Just a thought, I haven't got APT on this machine. Are you using RA/Dec J2000 in Stellarium and RA/Dec On Date in APT (or vice versa).

Also, once you have your target plate solved what is the reason for re-slewing to it?

Regards

Graeme

I've been re-slewing after sync to check and see if the target was still centered after centering, it never was. Now I understand why. Thank you.

[AstroBee]

Orthogonality could be your problem too...

But still, don't re-slew after you plate-solve. Re-slewing is basically telling the scope to go back to where it was before the plate-solve & re-center.