Help to with improving my RA RMS guiding numbers.

[G Ha]

I am running an AM5N with a Redcat 71 and ASI174MM guidescope on a pier at Starfront.  When I had the rig at the house on a tripod in Bortle 6+ skies I typically saw guiding at .5-.8 RMS.   After the setup at Starfront I checked the PA with TPPA and it reported about 2’ of alignment.

I am getting RMS in RA in the .9 – 1.2” range with the RA 2X the DEC RMS.  DEC looks fine in the graphs.  Calibration runs on the two axis are right on the money.  Yet I’ve been unable to reduce the RA.

Numbers in a couple of runs have had the RA peak to Peak as high as 22 arc sec, PA 5 arc-min.  Very inconsistent and RA gets worse over the exposure run time.

While my images (stars) look good at 300s subs I’d like to make sure that I can’t dial it in a bit better.

Thanks in advance.

Gary

https://openphdguiding.org/logs/dl/PHD2_logs_NSWe.zip

[Brian Valente]

Hi Gary

you seem to have a good handle on what's going on here.

Generally i would offer the following:

- calibration is fine

- there don't appear to be any constraining mechanical issues, it's just wandering about. Increase your RA aggressiveness, with lower exposure time and/or higher RA aggression setting. 

- one problem here is your guiding setup has a pretty coarse image scale of 10"/pix, so you are at or over the limit of what you can do there. You might consider a guide camera with smaller pixels. 

- the other related problem is your min moves are around 1", so not surprised it's wandering around in there. You probably want to be closer to 0.5" for the min moves, but your coarse guiding setup may not be up to the task. it's worth trying though

- on the mechanical side, there is an uncorrectable error at 143.3 seconds around .45" so that is likely constraining RA performance. However, with the strainwave and more aggressive cadence, you may be able to better address this in guiding. 

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[G Ha]

Thanks Brian.

The Frequency chart you show was from log 13.  If you look at log 14 it looks like what I think would be a good chart with the peak at 288s.  Log 13 pre-meridian flip and Log 14 post flip.  Is that normal?

I'll try higher RA aggression.  I had been running.5s exposures with similar results, though the aggression was still at at at 31.  

I'll post a followup after the skies become free of frozen precipitation, looks like that might take a few days...

[G Ha]

And I should have asked would running PPEC be of any benefit?  

[Brian Valente]

Gary

Segment 14 was on the opposite side of pier and seemed to be the outlier by far. All the others looked very similar to 13. So you may have something shifting or sagging when you flip sides of pier 

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