Unstable guiding despite a good night

[Eric Giraud]

Hello

I just unexpectedly had a very bad guiding night, while the sky was clear and there was no wind at all.

I did a calibration around the equator as a consequence (usually I would live with the previous one) and even one at the target location at ou despair.

I use an EQ6-R pro mount with ana OAG mounted on my C11 (with 0.7x reducer), the guiding camera is a Xena-M 585.

Please find attached the log for the night: https://openphdguiding.org/logs/dl/PHD2_logs_gPxX.zip

For instance I have a very bad frame at Time 2-35-37 while sky conditions were great.

Many thanks for you support.

Cheers,

Eric.

[Brian Valente]

Hi Eric

this looks like quite a mess. Despite a few recalibrations, the results are inconsistent and all over the place. You received calibration eror messages that the rates were different from expected, but that wouldn't explain what the log shows. There is one exception to this: in example you specifically mention at 2-35-37 and a few other places it shows you likely locked on to a hot pixel. Consider using a dark frame library.

I don't think this is a guiding or PHD2 issue. It looks to me like something may have gotten loose in your imaging train or mount. I suggest you revisit your imaging train and mount clutches and check to make sure everything is tight, nothing has come loose. I suggest you next test by not changing the rotator angle, using calibration assistant followed by a few minutes of guiding assistant and have it measure backlash. See how it goes

Brian

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Brian Valente

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[Bruce Waddington]

I agree with Brian, this isn't really a guiding problem, I think something is fouled up in the payload on the mount.  Can you give us some more context here?  Is this a permanent setup, is it local or remote?  How long have you been using the rotator and do you know that the rotator works correctly with guiding?  What changes have you made since the last time you were getting good results?  Problems like what we see here are pretty clearly coming from the gear riding on the mount or related cable routing problems:

Notice that the big excursions can happen on either axis.  This is especially interesting for Dec because the Dec motor often wasn't even running when the excursion began.  If you're new to using a rotator, you have to be careful that rotation doesn't create wrapped cables.  Going forward, when you get an acceptable result from the Calibration Assistant, keep using the calibration.  Otherwise you're probably just starting to flail around.

Good luck,

Bruce

[Eric Giraud]

Hi Guys,

Thanks for the help. Back from a business trip and testing again. I am using a Pegasus Astro rotator that I have already used on my Epsilon 160ED with success, but for the first time on my C11 and yes in an OAG format. My mount is an EQ6-R pro, in a fixed set up outside.

I have checked for potentiel strain in the cables and for any loss components. Found nothing wrong.

The balance of the mount is as good as I can do.

And there is no wind.

The other new element is the use of a Xena-M 585. I first was using the Ascom driver and I changed for the native Player One driver. That didn't help.

I also changed the guiding speed from 0.9 to 0.5, no change.

I also get all the time a "Star not found" while the SNR is way above the minimum threshold and HFD values of the stars well within limits (see picture attached). That must not be helping the guiding system to manage stability.

https://openphdguiding.org/logs/dl/PHD2_logs_VuKw.zip

Cheers,

Eric.

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[Bruce Waddington]

I don't think we have much to work with here and I'm not really clear on what you're doing.  We can start with the obvious stuff which is why you're getting lost-star events.  These all started after you began to horse around with the Max-HFD setting in PHD2 which you reduced to a level where seeing-enlarged star images were getting rejected.  Why were you fiddling around with this setting?  Next, you added a rotator to the configuration in the middle of trying to diagnose problems with the existing setup.  Doing this should have meant you needed to think through the correct setting for the 'reverse sign of angle' property of  the rotator in PHD2 but there's evidence in the log that it isn't correct.  In your Newtonian setup, I would guess you have an even number of mirrors in the optical path to the rotator but if you're using an OAG with the bigger scope, you probably have an odd number of mirrors.  Each mirror in the optical path is a point of reversal in the image.  You're continuing to struggle to get clean calibrations which means the subsequent guiding sessions are suspect.  The only guiding sequence of any useful length - 16 minutes - was done with the scope pointing down in the weeds at an elevation of 30 degrees.  At that point, the scope is looking through 2x the air-mass compare to a pointing position close to the zenith - so it's no wonder the total guiding rms was 1 arc-sec.

I think your setup has mechanical problems that need to be sorted out.  The Dec axis, in particular, doesn't appear to respond predictably to guide commands and I suspect the axis doesn't rotate smoothly and repeatably in all possible pointing positions.  Perhaps you can get some advice on how to mechanically tune the performance of that axis - it's not something that can be "guided out" very effectively.

Good luck,

Bruce

[Eric Giraud]

I think there is an issue with my mount indeed. 

And btw I don’t understand where this statement is coming from: « you added a rotator to the configuration in the middle of trying to diagnose problems with the existing setup »??

Eric. 

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[Bruce Waddington]

Sorry, perhaps I misinterpreted this statement: " I am using a Pegasus Astro rotator that I have already used on my Epsilon 160ED with success, but for the first time on my C11 and yes in an OAG format."

In any case, I don't think the 'reverse' setting is correct at this point and you might find it easier to work through the basics without having the rotator being actively used.