Newbie Guiding (Feature Tracking) Question

[BillR]

I'm relatively new to SharpCap (but very experienced at deep sky imaging with NINA). I've been trying to get into planetary imaging and just started using SharpCap, so I'm still on the steep part of the learning curve. While using SharpCap's Feature Tracking the past few nights on Saturn, it keeps Saturn centered nicely in the ROI, but eventually Saturn migrates out of the sensor frame and I find I'm taking images of blackness. I cannot figure out what I'm doing wrong.

The mount is polar aligned and without Feature Tracking enabled, it keeps Saturn in the frame for over 2 hours. So I clearly have something configured incorrectly with Feature Tracking that is causing it to slew out of the frame in 10 minutes or less. I can also hear the mount making adjustments almost every second, which is strange.

I'm using a CEM40 mount with an EdgeHD 8, 2x Barlow (so effective focal length of ~4000mm), and an ASI585MC camera (3840×2160). My Feature Tracking settings are shown below. Calibration was successful. I've been using an ROI of about 1000x1000.

Feature Tracking.jpg (57.29 KiB) Viewed 39 times

Any help would be greatly appreciated.

Best regards,

Bill

[admin]

Hi Bill,

it's worth watching the movement and correction graph when you are trying to solve this sort of issue - that shows both how far the planet appears to have moved according to the the measurements being made and the corrections that have been sent to the mount to try to get it back in position.

Given you mentioning that the mount is correcting very frequently, the first thing I would try is to increase the 'dead zone size' - that's the area around the desired position that is considered 'good enough - do nothing for now'. If that is too small then the tracking can end up trying to follow random image movements caused by the seeing, which is not desirable.

If the movement seems to be oscillating - first one direction then the other, with corrections being applied in both directions then try turning down the 'correction scaling' to something like 50 or 60%

Another possibility is that your mount is trying to apply backlash corrections to each movement - those can misbehave for small movements, meaning that the amount moved doesn't turn out to be the amount SharpCap asked for. You could try changing the movement speed to 'guiding rate' - that usually avoids any backlash compensation from the mount firmware, although it might struggle to keep up with rapid drift. The bigger dead zone might help here too - it would mean fewer but larger corrections.

Hope this gives you something to try,

Robin

[BillR]

Thanks for the timely reply. I was out again last night because the seeing was supposed to be pretty good. Oddly, I did not experience the same behavior as before even though all the settings were the same. I was able to take images for over an hour without the target sliding out of the frame, and the mount was not making continuous adjustments. I don't know what changed.

BTW - I already had the "Correction Scaling" set to 1%, so it cannot be reduced any further. And my iOptron CEM40 mount doesn't have any built-in backlash compensation - that must be handled by the tracking software.

Thanks again,

Bill