Fusion 120i Alt-Az – Feature Tracking calibration fails on one axis

[Planetpete]

Hi Robin,
I'm trying to get SharpCap Feature Tracking working with a Sky-Watcher Fusion 120i Alt-Az mount and Skymax 150, using an ASI585MC.
The calibration consistently fails on one axis. One direction moves normally, but the opposing direction produces little or no observable movement and calibration then fails with inconsistent scales or inconsistent angles.
I've tested this using:
SynScan control
GS Sky Telescope ASCOM
On Camera ST4, with the ASI585MC connected directly to the Fusion's ST4 port
All three show essentially the same problem.
With ST4 I received:
“Inconsistent angles between axes measurements (162.10°, should be about 90°)”
I'm wondering whether the Fusion's normal Alt-Az tracking is interfering with the Feature Tracking calibration movements. In particular, one direction appears to move against the mount's normal tracking, while the opposing direction is effectively being fought by it.
Does SharpCap account for the mount's ongoing tracking during Feature Tracking calibration on an Alt-Az mount, or should tracking be stopped during calibration?
I'm trying to establish whether this is a SharpCap calibration issue or an interaction with the Fusion 120i/SynScan Alt-Az tracking implementation.
Thanks,
Pete

[admin]

Hi Pete,

I think the most likely cause is going to be the interaction of the two movements - the Alt-Az mount probably stops tracking while performing the axis movements requested by the calibration, and it's almost impossible to know how much tracking distance is lost (for instance the time between tracking stopping and resuming is most likely longer than the time spent moving the axis). Unfortunately the interaction between tracking and the axis movements is not really handled uniformly across different ASCOM mount drivers (and often not handled in accordance with the ASCOM specification either...)

There are some things you can try that can help deal with this

1) Try calibrating using a faster movement rate - this increases the chance of getting good, measurable movement even if the mount is losing some of the movement due to the tracking being lost for some of the time

2) Try using the 'Continuous Movement' rather than 'Stepped Movement' in the Calibration settings area - this causes SharpCap to try to calibrate in each direction using a single, non-stop movement, which can help a lot with this sort of problem

3) If available, try using the guiding rate option for the movement speed - this causes SharpCap to use the mount's pulse guiding system (rather than the axis movement system) to request movements. It's slow, but it should add on top of normal tracking properly (if the mount supports it - I would expect EQ mounts to do so, but less obvious for AltAz mounts).

Hopefully one or other of these suggestions will help.

cheers,

Robin

[Planetpete]

Thanks Robin for your advice.

Please see attached the settings which worked for me.

Cheers

Pete