Drift Graphs and PEC
Posted: Sat Apr 13, 2024 7:42 pm
I’m probably obsessing too much but am wondering if these drift graphs from Live Stacking are showing good/bad/expected tracking from my mount (Skywatcher HEQ5 Pro). I am getting good clear images from SharpCap Live Stacking, so I suspect that everything is ‘good enough’ for EAA.
I always get the SharpCap Polar alignment error to less than 1min, Good, and occasionally Excellent.
The two images are made from replays of raw frames, both around 10 minutes total exposure, one at 4s, one at 8s. My camera orientation is such that RA is approximately up and down, Dec is left and right. As I watch the frames replay, the latest position seems to move cyclically – up to the top, then down to the bottom, then moves up again. There's a clear matching pattern in the two drift graphs, with each of them starting at a different position in the cycle. I’m guessing that this is due to periodic errors.
As I understand it, the scale of the drift graph is in pixels, and it looks like I’m getting about 45 pixels drift in the Y direction, which corresponds approximately to RA. I think that the angle must be because my camera isn’t quite aligned with the OTA axis – plate solve reports ‘Orientation : up is 262.1 degrees E of N’.
With an ASI585MC on a Skywatcher 200P, the FoV is approx. 0.64deg x 0.36deg, so at 3840x2160 pixels that seems to be 0.6arcsec per pixel, a total drift of 27arcsec, or near enough half an arc minute. I’m wondering if that is expected for this mount.
Which then leads on to…if this is due to periodic errors, does SharpCap support PEC, or do I need to do it outside of SharpCap using EQMOD for the PEC training? And does anyone else here use /recommend PEC for EAA Live Stacking, or is it just chasing improvements for minimal return?
Cheers
Geoff
I always get the SharpCap Polar alignment error to less than 1min, Good, and occasionally Excellent.
The two images are made from replays of raw frames, both around 10 minutes total exposure, one at 4s, one at 8s. My camera orientation is such that RA is approximately up and down, Dec is left and right. As I watch the frames replay, the latest position seems to move cyclically – up to the top, then down to the bottom, then moves up again. There's a clear matching pattern in the two drift graphs, with each of them starting at a different position in the cycle. I’m guessing that this is due to periodic errors.
As I understand it, the scale of the drift graph is in pixels, and it looks like I’m getting about 45 pixels drift in the Y direction, which corresponds approximately to RA. I think that the angle must be because my camera isn’t quite aligned with the OTA axis – plate solve reports ‘Orientation : up is 262.1 degrees E of N’.
With an ASI585MC on a Skywatcher 200P, the FoV is approx. 0.64deg x 0.36deg, so at 3840x2160 pixels that seems to be 0.6arcsec per pixel, a total drift of 27arcsec, or near enough half an arc minute. I’m wondering if that is expected for this mount.
Which then leads on to…if this is due to periodic errors, does SharpCap support PEC, or do I need to do it outside of SharpCap using EQMOD for the PEC training? And does anyone else here use /recommend PEC for EAA Live Stacking, or is it just chasing improvements for minimal return?
Cheers
Geoff