So last night was quite a desaster
I'll still have to go through the logs, which is somewhat a mess as PHD2 kept crashing a lot.
But the essence is that if I run unguided there is a drift of ~1.2 arcsec per minute in RA. I have no idea where that is coming from. ISTR someone had mentioned a similar issue in the firmware update thread - will have to look for that.
The drift-corrected errors in that unguided phase seem reasonable - something like an arcsec PtP, so around 0.3 RMS. But as soon as I start guiding it begins to oscillate, amplitude increases to 2.5-3 arcsec PtP, RMS 1 arcsec. While this might sound not too bad, it is (persistently over many hours) a factor 4 larger than the DEC RMS. The spot diagram doesn't even look like a football - it's a cigar.
I had experimented throughout the night with various guide algorithms, aggressiveness settings, exposure times. Some settings seem somewhat better than others, but never did I get substantially below 1" RMS.
One of the unguided periods suggested that there was no 5.5s peak at all - only a 2.8s one. That one is also visible in several other power spectra, together with the 5.5 one. I wonder if that is the base and 5.5 is a harmonic? I had tried 2s exposure and adjusted the 'Time Lapse' to get a 2.8s update frequency. My impression was that was one of the better settings.
Maybe someone has additional input/suggestions - would be highly welcome. I'll post more details with logs later. Right now I start wondering whether I should better have gone for the non-EC one
Sounds like you are experiencing exactly what I have been gong through with my 6 month old CEM60EC...
1. Guiding in DEC is excellent
2. Unguided tracking is excellent with low RMS (0.3 arc-sec) but there is a slow steady drift. I just discovered that recently.
3. RA guiding goes crazy with completely random large amplitude excursions not related to seeing that will not damp out. I have tried long guide durations high min motions and low aggression and everything in between and nothing will produce consistently good RA guiding.
You and I are not the only ones to see this. There are other posters saying they essentially gave up RA guiding their CEM60EC mounts and guide only in DEC or just run unguided. The mount can do very well unguided, but then dithering becomes an issue. I did not buy the mount to only use for unguided imaging. I venture we both bought our mounts expecting them to effectively guide in RA.
And the strangest thing is that the very first time I used the mount 5 months ago, it guided great in both RA and DEC the first night! It has never again guided well in RA since that first night. This strongly leads me to believe the solution will have to be software/firmware related.
Edited by John Miele, 28 June 2019 - 12:30 PM.