last time I used my equipment (Oct 2021), everything worked fine. Guiding was very good, as it had always been (tot rm ~0.5).
Then I had to send my imaging scope away for repair, so I did nothing up until Feb 2022. I took everything out again (I setup and teardown every night) to do a test session and, while focus, imaging, aligning, etc worked super fine, guiding was a nightmare.
The tot RMS was constantly > 0.7, with peaks to 1.3. I thought I did something wrong, so I called it a day and stopped the session.
Then yesterday night I went out for another test session. This time I did everything perfectly (very good PA, mount 3D balanced), but the guiding results were awful again. It's was like guiding was unstable, tot RMS went from 0.6 to 2.5 even though outside there was no wind (my mount is partially protected from wind though) or animals that could have caused that. I tried playing around with some parameters, but they didn't help much (probably because I don't know how to tune them).
* iOptron CEM70
* ASI290MM mini
* APM 50mm f/4.1 guide scope
* QHY268M + TecnoSky AG70 for imaging
* exp time 2.5-4s, then settled to 3s
* remove DEC backlash enabled
* Reset Guide calibration after each slew enabled
* pulse 1000
* max iters 3
* max move (px) 15
* two axis enabled
* gpg ra guider enabled and set to 348
* aggress 0.75/0.75 (I played with those values, some times it got better with 0.5/0.5)
* PEC is disabled
* Kstars 3.5.7-stable and INDI 1.9.4-stable on openSUSE
I honestly don't know what to do to improves things. I've tried PA with iPolar + EKOS, only EKOS, only iPolar. I've tried 3D balanced, a bit unbalanced, but couldn't get the very good guiding I had last year and suggestions/tips for me?
I'm sure you've gone over things several times, so this might not be to useful. but when I experience these things, I start over with the basics, checking the mount to ensure everything is tightened dow, checking the telesopes ensuring they are tightened down, check the cable drag, and rechecking balancing. Also, based on PHD2 best practices, I leave the RA axis slightly off balanced - getting the system too accurately polar-aligned can result is some eratic behaviour in RA.
@Ron: seeing could worsen the thing, indeed, but I don't think that such bad behavior is only due to seeing. Or maybe it is and I'm chasing ghosts, who knows
I didn't run PHD2 guiding assistant, but I did guide with PHD2 (to check that EKOS wasn't the issue) and results were similar.
@fmozza: that's whay I did this morning. I tightened things down, improved the 3d balance (it was a bit off in dec), checked cabling. I've read online that the CEM70 seems to prefer faster exposures, so tonight I'll try again with 1.5s.
Also, if I make it east heavy it won't work after a meridian flip (which I usually do unattended)
Question: I see that PHD2 wants to calibrate at meridian-equator. EKOS doesn't ask for that, so I let it calibrate wherever I am (e.g. Ursa Major area, if imaging M51). How do you calibrate guys?
I don't have a CEM70 but it would be useful to see screenshots of the Guide settings, calibration results and guiding results. These might help us see if its an RA or Dec (or both) problem and might give us more clues.
I think the PHD folks recommend calibrating near the interaction of the Meridian and Equator as this is where you'll get big pixel movement on both RA and Dec axes for a given guide pulse. In other parts of the sky you won't get as big pixel movements so the calibration will be less accurate. This isn't specific to PHD, its also how the EKOS internal guider works.
So if your mount responds predictably in all areas of the sky you'll get better results by calibrating at the Meridian / celestial equator. If your mount is a bit less predictable you might get better results calibrating in the area of the sky you're actually going to be capturing in.
Attached there's the analyze file for yesterday's session.
This time I was perfectly 3D balanced, and things went better than yesterday. Still, RMS was far from being as good as it was.
Things got a bit better when I pointed against IC1805 (N-W) compared to when I was pointing against Alioth (N-E).
In our experience with a range of mounts, it is the seeing which is the major contributor to the guiding. Even during a session the guiding can become worse or better.
It's a pity we don't have a guiding assistant to set minimum RA and DEC errors (ME). We tend to eyeball the seeing by observing a star e.g. when you focus at the start of a job. If it's bouncing around, we use say ME of around 60. If it's steady, leave it at the default 20. As @RON CLANTON suggests above, you could always switch to PHD2 and try their guiding assistant.
You don't mention which guide algorithm you use, but if you haven't already tried it, multistar is the way to go.
If you really don't think it's the atmosphere, you're gonna have to pull the mount apart and clean, lubricate and adjust to eliminate the mechanical side of things from the guiding.
@Paolo its tricky to say but its worth as others have said to try the PHD2 guide assistant and see what that recommends. Also on the PHD2 website they have some documents that explain common issues / problems, etc. So worth going through that.
I've only looked at 1 log and I'm not really an expert but something did jump out. When the Dec swaps direction it is often accompanied by a long period where the Dec stays significantly off centre. Here's one example...
In this example the Dec stays off centre for about 30 secs despite continued guide pulses trying to correct it. Then it returns to centre. So the question is... what's going on? This could either be because the backlash compensation on Dec isn't working very well or Dec has some stiction. The PHD2 guiding assistant would tell you about backlash. Also, in the internal guider there is a calibration setting to allow for backlash on Dec - but I think you had that turned on (from your first post).
So its worth running the PHD2 guide assistant and then spending more time on the logs to see if the Dec swap "issue" is a real consistent issue.
FWIW, I don't think your guiding is that bad, but as with mine, it could be improved. Good luck!
I'm in a similar situation with my CEM70. I was very happy with the guiding performance back in Sept before the clouds rolled in. I was consistently below 0.6" RMS on most nights, and sometimes significantly better. Lately I've been struggling to stay below 1.0 over several sessions.
I took a "back to basics" approach and did a careful polar alignment. Both Ekos and PHD log viewer report polar alignment error of less than 1'. I then checked all the bolts for tightness...all good there. Guiding was still not where I think it should be, so I turned off the RA and DEC checkboxes in the guiding tab to record the motion (using the internal guider), then turned both back on after a full cycle. I opened the log file in PHDLogViewer, see below:
The PE is much larger than it used to be.
Polar alignment is good as the DEC doesn't drift
Guiding is effective, even if the results aren't quite what I want. Entirely possible that seeing is to blame and I've just had consistently bad conditions.
I'm going to check belt tension and worm gear mesh on the RA side and try again tonight.
@John: thanks, I'll do that next time. I'll also try to bring my rig to another location near by, where I can point it to the South, so I can do a proper calibration. Maybe it'll help.
@Casey: thanks! I'll try the same experiment you did, I'm curious to see how my mount will behave. Please let me know if adjusting the mesh did help you or not! I would prefer to leave this as last resort TBH.