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Calling All SMA Guiding Experts and Expert Adjacent

Sky-Watcher EQ6-R Pro Equatorial Mount Guiding Troubleshooting
Southern Maine Astronomers •6 replies•46 views
Dean Ostergaard avatar
Dean Ostergaard avatar
In my latest gallery post I mentioned that I have been working out guiding issues with the club's EAA / AP rig.  I was ready to swear never to buy an EQ6R-Pro mount but now perhaps I think it isn't entirely the mount's fault.

Symptoms:
  • Mount did not respond to the guide pulse command
  • Calibrations results poor or unacceptable
    • e.g., DEC and RA backlash not orthogonal (Graph often shows an angle closer to 45 rather than the expected 90)
  • Runaway DEC axis (often followed by the error above)
  • Unable or too long to stabilize after a dither
  • Unable to resume guiding after a major mount movement (usually involving flipping to the other side of the pier but sometimes when changing targets on the same side.)

Issues I think I have identified:
  • Guide camera loses focus after a major mount movement
    • It's hard enough to focus as it is. The camera is held into the barrel on the ZWO OAG with a single tension screw (no compression ring) and does not fit snugly. It may be flopping around with big movements and no amount of cranking on the tension screw can prevent it.
  • Polar alignment is critical. At least on those nights when I was able to achieve decent guiding PA was within less than 1 arcminute.
  • Optical train flex or floppiness.
    • I noticed newer versions of this scope come with a different focuser. I wonder if it was to address this issue.

Bottom line right now is that reasonable guiding is achievable but requires a lot of babysitting, frequent recalibration, and active corrections as described above. This isn't a rig you can just hit the play button on and go to bed until it's time to take flats.

I intend to swap out the club imaging train with my own Player One Camera, Wheel, and OAG which are all very solid and held together with 6 screws at each interface rather than the more common M48 screw-on. The OAG has a helical focuser and a much larger prism which should help. This won't cure the optical train flex but may help a bit, especially if I don't have to constantly manhandle it to refocus after every movement.

Nothing here addresses any issues there might be with the mount itself but maybe the mount is the victim of these other issues.

I am putting all of this here in case other club members have any ideas or suggestions. I think I can find PHD2 guide logs to post if anyone is good at analyzing those. I've looked at them but all they tell me is that the guiding sucked.
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Jeremy Wright avatar
Jeremy Wright avatar
What is your typical RMS when things are running well?

Email me the guide logs, no promises but I'll look.

Some initial observations:
- oag should prevent flex issues if all of the oag parts are screwed tightly together
- helical focuser is a huge help w focusing guide stars, which is important
- any focuser flex should be very slow or intermittent, and with an oag I wouldn't think would routinely affect most subexposures
- that rig did get knocked over onto pavement once, and you are probably the first person to attempt serious long exposure AP with it since, so loose parts are definitely a possibility
- your AM3 should handle the 115 with a counterweight and would make for a nice control to see if the issues are mount related or something else
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Dean Ostergaard avatar
Dean Ostergaard avatar
Hi Jeremy,

I have attached 3 log files here in case anyone else here wants to take a stab at it the logs from 4/17 & 4/20 are pretty bad, I included the log from 4/23 as well because that was a pretty good night where I watched and tweaked closely through most of the night. That was the night I shot the Pinwheel.

The flex seem to come primarily from the two rotator rings on the scope & focuser. There is one that allows rotation of the entire focuser draw tube assembly. The other is at the end of the draw tube that allows rotation of the camera and accessories (basically everything behind the draw tube). 

Contact with the pavement is evident from a couple of blemishes on the scope tube and dew shield but I don't see evidence that the scope was harmed internally, At least nothing that can't be attributed to the obvious flex from the focuser and back.

I have Green Swamp Server installed on the miniPC. Had considered doing the PEC training but decided that probably wouldn't help much until the other issues can be addressed.

PHD2_GuideLog_2025-04-17_162413.txt PHD2_GuideLog_2025-04-20_201928.txt PHD2_GuideLog_2025-04-23_165107.txt
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Jeremy Wright avatar
Jeremy Wright avatar
So I'll preface by saying I'm certainly no ace at reading guide logs, but a few observations:

1.  You have some long periods of relatively good guiding 0.8 - 1.0" rms.  You should probably be able to get that mount to 0.5-0.8" on nights of fair to good seeing.

2.  The deviations to me look like a mixed bag, some periodic error, maybe a few "events" like cable snag or wind gust

3.  Your camera gain is pretty low at 50, you might be able to pick up more guide stars (and make seeing less of an issue) by cranking up to 300

4.  Your exposure time is on the long side, which is okay if periodic error isn't too bad, but will be slower to correct for those "events" above.  I always found the sweet spot with my CGEM to be around 2 seconds.  (Jealous of Astrophysics mount owners and their 4-5' guide exposures).

I would also suggest to go ahead and try to train PEC and then see where things stand.  It will make your guide setup work less hard at correcting PE.  But definitely use multiple cycles not just one for training.
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Dean Ostergaard avatar
Dean Ostergaard avatar
Thanks Jeremy!

There were some periods of good guiding but I feel like it took a lot of coaxing to get them. Like, the DEC would run off and I'd stop and restart guiding to reset things. That's why there are a lot of shot duration log sections.

I was trying the longer exposure to average out the seeing. I never even thought to change the gain. I left it as it was from whomever set it up before.  I can almost guarantee there were no cable snags but wind was definitely an issue one night, I don't remember which.

I'll try your suggestions. If it looks improved I'll train the PEC and see where we can get this.

Thanks for your help!
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causalityCat avatar
causalityCat avatar
Not sure this thread hasn't gone stale. There have been so very few clear nights that it is likely the night you imaged was the same night I was imaging when there were very big gusts of wind. Before midnight, the scope (7" MakNewt) was being thrown around to the tune of arc  *minutes*. Guiding was not possible with many 'lost star' notices.. Well after midnight the wind calmed down enough to guide and image.

Since that night, have you been able to guide effectively and in the expected manner?
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Dean Ostergaard avatar
Dean Ostergaard avatar
It hasn't gone stale but like you said, not many clear nights.

I was definitely out on that windy night and realized the wind was making it impossible.

I was out one other night on the 28th. Conditions were a bit better wind wise. On that night I did manage to get it to guide a bit better, 

I had swapped the image train for one of my own but that didn't remove all of the flex. I had to refocus the guide camera after the flip by 1 or 2 marks on the helical focuser. I'm wondering if the flex is along an axis that moves the OAG prism in or out enough to cause that.

I also implemented the suggestions Jeremy made. It was a better night but it still required a lot of babysitting. Still getting some "no response to guide pulse command" errors and the DEC drifted off at least once. Went through calibration a few times at the beginning of the night before I got one it didn't complain about.

I think I may swap the Astro-Tech to my AM3 to see how it does there although that Kingdell PC weighs a ton compared to my MeLE so I might be pushing the limits. If I do that I'll swap my little Draco62 to the EQ6R-Pro to see how that does.