Mount missed the target co-ordinates

[pmohan]

Did not find this specific topic in my forum search. Apologies if covered before...

Getting a new Losmandy G8 and vintage TeleVue 101 + Ares-M integrated with latest version of Sharpcap. Mount connects to Sharpcap and Polar alignment goes well with solid star tracking. While testing GOTO on some targets, I've been getting the message below when attempting to slew to a specified RA/Dec using the 'GO to catalog/target coordinates' tool :
******
Debug 22:07:48.207163 #1 Sequencer : Info : 'Mount slew complete, waiting for mount to settle.'
while running step Move the mount to (RA,Dec) 00 39 0,86 0 0 (RA=00:39:00.0,Dec=+86:00:00)
in void SharpCap.Sequencer.SequencerContext.OnProgress(string e)
Debug 22:07:53.828092 #1 Notification (Status=OK): The mount missed the target co-ordinates by 0.1° -
expected to arrive at RA=00:39:00.0,Dec=+86:00:00, but mount ended up at RA=00:39:25.0,Dec=+86:08:35 after movement complete. in void SharpCap.UI.NotificationViewModel.DisplayMessage(NotificationMessage message)
Debug 22:07:53.828533 #1 Sequencer : Completed : Move the mount to (RA,Dec) 00 39 0,86 0 0 (RA=00:39:00.0,Dec=+86:00:00)
******
I've notice that the "0.1 degree" error reported is consistent over slew trials. While, with my 1.2 deg FOV, this pointing error is not huge, I'm trying to understand what's behind it and hopefully how to fix it. The message happens while the mount is well away from any limits. I'm aware of the potential issues with J2000 and JNOW but this seems a different thing, or maybe not?

Cheers, Paul

[admin]

Hi Paul,

the 0.1 degrees showing up every time is a bit misleading - SharpCap doesn't show the message at all if the offset is less than 0.1 degrees, and it shows the distance rounded to 1 decimal place, so for any offset between 0.1 and 0.15 degrees, you will see 0.1 displayed.

The goal of this warning is to flag that the mount is doing something unexpected, which might then have follow on effects if you are plate solving (it could lead to the plate solve failing to bring the mount to the right position). While it's expected that the *actual* position in the sky that the mount points to after a GOTO may not be what you were aiming for, the position that the mount itself reports should be correct.

It's possible that there are configuration options in the ASCOM driver for your mount that might be relevant to this - you could imagine that certain options related to pointing models or accuracy might have an impact. It would probably be worth exploring the options of the ASCOM driver to see if there is anything worth tinkering with to try to resolve this.

cheers,

Robin

[pmohan]

Thank you for your feedback Robin.
I'll check into the Gemini ASCOM driver options as you suggested.
Of late, the 'missed target ' warning is not occurring. I'm still working through the many setup permutations
to get repeatable alignment between GOTO plate solving & resync in SharpCap and what Stellarium indicates as the final mount location.
I'm sure there's ample room for operator setup error here but won't over stress on it. I'm also anxious to try out your Pixel Position/Click to Recentre tool to help my investigations.

-Paul

[admin]

Hi Paul,

good luck getting it sorted. One more thing to throw into the mix - there is a setting in SharpCap for how it does the recenter when using plate solving - look in the 'plate solve settings'. The default is to 'sync mount and recenter target', which works in most cases and should get the target in the middle of the view *and* the mount co-ordinates matching the target ones at the end of the operation.

However, for mounts that use the 'sync' operation to help build a pointing model instead of to optimize GOTO in the region of the sync (not in ASCOM spec strictly, but never mind), you may need to use the 'offset the mount to center the target' option. This works out how far off the initial GOTO is, then re-calculates the co-ordinates to GOTO that would put the target in the center of the image. With this, you get the target centered, but at that point the mount co-ordinates will not match the expected ones of the target.

cheers,

Robin

[pmohan]

Very good and thanks Robin. I will explore that path, and as well the mount driver option switch to tell the mount to 'Use J2000'.

Cheers, Paul