Goto catalog target and resync : Re-Centering is wrong

[LaurentLab]

Bonjour ,
Vers SharpCap : 4.1.14236
Windows 10
Telescope Dob 250 goto Skywatcher with dongle wifi Synscan Pro connected by ascom
When i do a goto catalog target (for example "denebola ") , at the end the object does not appear on my screen .
Note that the coordinates (Jnow ) displayed on the tracking window are accurate and I can manually re-centering my target with the arrows.
This problem didn’t exist last year, even though sometimes I had to do a second go-to to have the object in the center of the screen.
You can look at the log between 22:23:24.112 and 22:36:46.286, which concerns denebola’s goto
There is a difference of 3 degrees in declination
thank you in advance for your help and please excuse my English!
Laurent

[admin]

Hi,

there are two things I can see of interest in the log

1) In your first attempt to GOTO Denbola, when trying to recenter after plate solving, there is an error that the mount failed to arrive at the target. This looks like it might just simply be a glitch in the communications with the mount, as we see this in the logs

Code: Select all

Debug  	22:23:18.662493	#1 	Sequencer : Info      : 'Slewing, 0,0° from target at RA=11:50:26,5,Dec=+14:25:25' while running step Move the mount to (RA,Dec) RA=11:49:03.6,Dec=+14:34:19 (RA=11:49:03.6,Dec=+14:34:18)	
Debug  	22:23:18.666581	#1 	Sequencer : Info      : 'Waiting for mount to settle' while running step Move the mount to (RA,Dec) RA=11:49:03.6,Dec=+14:34:19 (RA=11:49:03.6,Dec=+14:34:18)
Debug  	22:23:18.669732	#1 	Sequencer : Info      : 'Mount slew complete, waiting for mount to settle.' while running step Move the mount to (RA,Dec) RA=11:49:03.6,Dec=+14:34:19 (RA=11:49:03.6,Dec=+14:34:18)	
Error  	22:23:24.095007	#1 	Running step Move the mount to (RA,Dec) RA=11:49:03.6,Dec=+14:34:19 (RA=11:49:03.6,Dec=+14:34:18) : Exception of type 'Exception' : The mount failed to arrive at the target co-ordinates (off by 46,2°). Expected to arrive at RA=11:50:26,5,Dec=+14:25:25, but mount finished slewing at RA=11:50:27,0,Dec=+60:34:43 

The first line above shows that the mount was reporting a position very close to the target near the end of the slew, then SharpCap waits a few seconds for the mount to settle, and in the last line we see the mount co-ordinates are reporting a declination of +60 degrees rather than +14, although tthe minutes/seconds values are very similar. Now, the mount is not going to have jumped by 36 degrees in declination in 6 seconds, so the final dec co-ordinate that is being read of +60 degrees must be an error. There's really no way for that change to happen inside the SharpCap code (unless you have something odd like glitches in the computer memory changing values), so it seems likely that the +60 degrees value came from the ASCOM driver due to some sort of communications glitch with the mount.

Recent versions of SharpCap raise an error when the mount fails to arrive within 1 degree of the requested target, as this usually indicates that something bad has happened. Older versions of SharpCap ignored this.

There is another case of this sort of odd jump in the co-ordinates of the mount that I found

Code: Select all

Debug  	22:08:41.656467	#1 	Sequencer : Info      : 'Slewing, 0,0° from target at RA=03:04:00,2,Dec=+89:22:35' while running step Move the mount to (RA,Dec) RA=02:31:49.1,Dec=+89:15:50 (RA=02:31:49.1,Dec=+89:15:49)				in void SharpCap.Sequencer.SequencerContext.OnProgress(string e)
Debug  	22:08:42.159328	#1 	Sequencer : Info      : 'Slewing, 49,3° from target at RA=03:04:00,2,Dec=+89:22:35' while running step Move the mount to (RA,Dec) RA=02:31:49.1,Dec=+89:15:50 (RA=02:31:49.1,Dec=+89:15:49)				in void SharpCap.Sequencer.SequencerContext.OnProgress(string e)

It's definitely worth trying to work out why this sort of glitch is happening as it will cause all sorts of issues.

2) Some of your plate solving attempts are failing - this is probably related to your relatively small field of view (0.53 x 0.30 degrees) and the fact that you are using the 'default' plate solve database in SharpCap that is only really designed to go down to about 0.5x0.5 degrees. You need to go to the plate solving settings page in SharpCap and download the 'Hi Res' database and then make that active, which should help. In a few cases the failure may be due to the low number of stars detected, which might indicate that a higher gain or exposure would help.

What I can't see in the log is any evidence of the plate solve/recenter failing to improve the positioning of the target when everything works OK. There are a couple of parts where you first do the GOTO + Plate Solve + Resync + Re-goto, then plate solve again, and the position is always close when the second plate solve is run.

cheers,

Robin

[LaurentLab]

Thank you very much for these very thorough explanations!

Laurent