SharpCap Forums

Dear all

My problem is similar to one posted elsewhere in the forum. But not sure if this was ever resolved. After a platesolve, which is successful, the stars immediately start to drift off target in the image.

Setup:
Mount: Sky-watcher Star Discovery AltAz mount
Scope: 150p flextube newtonian
Driver: Synscan
Camera: ZWO 585Mc
Software: Sharpcap + Stellarium

Mount is set to use synscan app in hardware settings inside sharpacap (although I have also used ASCOM device hub with same problem). Platesolve setting set to sync and recenter. Tracking set to sidereal in mount controls.

Problem:

After aligning the scope using synscan, I then use platesolve in sharpcap to refine the pointing, which is successful. I'm using the native sharpcap platesolving engine (which is excellent BTW). Unfortunately the mount immediately begins to go off target and stars drift off position, despite selecting sidereal tracking in the mount controls in sharpcap.

I can get around this by returning to synscan app after platesolve, reperforming the goto with the new synced Alt-Az coordinates, and clicking point and track. Then returning to Sharpcap, the image is steady and I am able to acquire images. Therefore it is not cable snagging. The mount is able to follow the target.

However this is unsatisfactory as I would like to use the platesolve and recenter option during a livestacking. However, using this would cause the mount to drift again and I would need to continually switch to synscan and perform the re goto and point etc.

Because I can't use that, the field rotation effect in the stack of imagies starts to crop the target too severely in longer exposures.

I believe it is also not dithering as well, because I am getting walking noise in my captures.

Any suggestions or advice would be greatly appreciated!

Thank you

Hi,

Firstly, general advice... Make sure you have the very latest version of the Synscan App and ASCOM driver installed - it's just possible that if you are using an older version then an update might fix this issue. Similarly, make sure you have the latest version of SharpCap.

Otherwise... I have a few questions that I hope will allow us to narrow down where the problem might be occurring...

1) Does the drift carry on for ever, or does it drift a certain amount and then stabilize? If it is the latter then the drift may be the mount taking up a certain amount of backlash after the GOTO movement.

If the drift carries on for ever...

2) Is it at the same rate that you see if you deliberately turn off tracking? (probably, but best to check)

3) Can you persuade it to restart tracking in any way from inside SharpCap without doing a re-goto? Turning tracking on/off in SharpCap, changing between the tracking modes for sun/moon/stars, etc? If there is a way then it might be possible to put some sort of code in SharpCap to automate what you are doing manually, but SharpCap is less likely to be able to automatically trigger things that have to happen inside the Synscan App.

Otherwise, feel free to share a SharpCap log that was created in a session when the problem occurred - there may be something unusual in the log that points to a cause.

Finally, you might want to investigate using 'Green Swamp Server' as an alternative to the Synscan App - it's a bit like a modern version of EQMOD and it may be that it is not affected by whatever is causing your issue.

cheers,

Robin

Hi Robin, thanks so much.

To respond to your points:

1) Does the drift carry on for ever, or does it drift a certain amount and then stabilize? If it is the latter then the drift may be the mount taking up a certain amount of backlash after the GOTO movement.

I have tested this with waiting five minutes for the mount to settle - the stars continue to drift without sign of steadying


2) Is it at the same rate that you see if you deliberately turn off tracking? (probably, but best to check)

Apologies, I should have mentioned that I did indeed try this, and the drift rate increased noticeably when I disabled sidereal movement. So that must be a clue.

3) Can you persuade it to restart tracking in any way from inside SharpCap without doing a re-goto? Turning tracking on/off in SharpCap, changing between the tracking modes for sun/moon/stars, etc? If there is a way then it might be possible to put some sort of code in SharpCap to automate what you are doing manually, but SharpCap is less likely to be able to automatically trigger things that have to happen inside the Synscan App.

I also tried this, and it did not fix the problem.

Otherwise, feel free to share a SharpCap log that was created in a session when the problem occurred - there may be something unusual in the log that points to a cause.

Thank you, I will dig out the log when I am back at home. I'll also checkout the green swamp server and report back next clear sky.

Much appreciate your reply,

John

Hi

I have not been able to resolve this, but for the sake of anyone else who has this problem, I am attaching a logfile from a session where the problem occurred. I am not sure if it is relevant at all but I see that the log records that there is a difference between system and mount sidereal rates. (The "system" being Sharpcap?)

I did however switch to GSS instead of Synscan to drive the mount. What a difference. Eliminated the drift and held the image steady, nailing the target to the centre so I could use the platesolve during livestack feature until it went behind the trees, for over two hours with no dropped frames. i'll stick with this from now on.

For those using Skywatcher Alt-Az mounts, I had to use the latest beta release of GSS (as of 15/9/2025) for it to work. The latest stable crashed when using the hand controls.

Thanks,

John

Hi John,

well, I'm glad to hear that using GSS turned out to fix the issue

I had a quick check of the log to see if something I had wondered about was happening (the mount perhaps not allowing Slew actions to RA/Dec co-ordinates in AltAz mode and forcing SharpCap to drop back to requesting a Slew to Alt/Az). That would have shown up with some distinctive log messages if it was happening, and they weren't there, so it wasn't happening. That was the only even half way reasonable thing I could think of that would/should make slewing affect tracking rates, so I haven't got any more to suggest on why Synscan App breaks in this situation (except to switch to GSS!)

cheers,

Robin