First time OAG user (ZWO OAG-L)

[Clayton Yendrey]

I just installed my first OAG (ZWO OAG-L) on my rig.
Esprit 100ED, SB MyT mount on pier, ZWO ASI2600MM imaging camera with ZWO EFW 2"x7, and ZWO ASI290MM Mini guide camera.

I reduced the aggression on both DEC and RA which seemed to help smooth out performance but I'm still getting RA excursions out to1"+ that don't appear when I run a PEC or the Guide Assistant.  

While I can't exclude the mount, I can't exclude my PHD2 setup/tuning either yet.

Can you please review my logs and see if there are any recommendations on my tuning/guide algorithm choice?

Thanks,

Clayton

[Brian Valente]

Hi Clayton

>>>>that don't appear when I run a PEC

can you clarify what you mean by this? When you are testing your mount performance it's a good idea to test without any mount-based PEC first

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[Bruce Waddington]

I don’t see much to get excited about here.  1 arc-sec excursions are hardly unusual and aren’t likely to have any effect on your images when they are quickly corrected.  They are not the result of guiding so the changes you made only made the situation slightly worse.  By reducing the aggressiveness, you’ve basically said when one of these excursions does happen, just take some extra time to react to them.  When guiding at this image scale with a mount that is essentially well-behaved, you can’t make intelligent choices about guiding parameters on-the-fly while squinting at the real-time guiding graph.  You should learn how to analyze the logs using PHDLogViewer and look closely to see what is cause and what is effect.  It’s quite likely that seeing is contributing to the tracking behavior you’re looking at and if you look closely you can see Dec excursions that are also fairly spiky. 

 

https://openphdguiding.org/tutorial-analyzing-phd2-guiding-results/

 

If you really want to worry about your guiding, you could consider these two larger excursions in RA (red):

 

 

 

Again, neither of these is caused by guiding.  If you have just switched to an OAG, you probably had to do some cable-routing for the guide camera.  If those cables can rub across a stationary surface or pull on the guide camera by 4-5 microns, they can create these excursions.  They can also contribute to smaller excursions depending on the details.  This is particularly true if the cables have ties on them or are encased in ribbed-plastic tubing. 

 

Personally, I wouldn’t worry about any of this until I could show it was having some significant impact on my imaging.

 

Regards,

Bruce

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[Clayton Yendrey]

Brian,
I performed a PEC last month as part of troubleshooting when the mount actions/performance suffered a few days of insanity.  I had guided with the usual good/great performance for the previous two days, on the third day it wouldn't guide withing 2" ttl RMS error.   I tried a new T-Point model had RMS error circles out to 9999" for the outer band and 4000"+ for the inner ring.    I looked at, tried everything I could think of to see what had changed and finally, as a desperation move, completely disassembled everything looking for something/anything that might have come loose, rubbing, etc.  Didn't find anything.   Tpoint and the following actions are all in TSX with the primary OTA/imaging train providing hte input, not the guide scope.

After reassembly, ran a new PA, then a new PEC as an additional diagnostic.  NO abrupt movements or spikes (a 5 worm cycle PE) just the normal mechanical 'noise' but nothing that would stand out (unlike last year when I had a RA worm assembly failure).  Uncorrected PE was 4" p-p according the TSX PEC Tool, corrected PE was reported as immeasurable, when sort a means 1"p-p or less according to discussions in the SB forums.  5 worm cycles recording the PE, the 5 worm cycles verifying its application/correction results is a 1(ish) hour unguided session recorded in TSX, monitored live on the image recording (1s imaging) and I always turn on the cross hair/sighing circle in the image so I can gauge the target movement more accurately.  After the 40 minute initial uncorrected PE recording, the target star was just off the cross hairs but still in the target circle.  Correction applied cross hair was still within the image of the star but no longer centered.  After that recorded a new 204pt Tpoint model which noted that PA alignment in az and el was excellent.  The T-point model did indicate strongly some n-s vertical stringing but in the discussion with SB it was decided that was due to the reduced tension in the DEC plungers that was to address the mechanical RA/DEC xtalk this mount has.

My first guide attempts (still using the external guidescope) were back to similar, but not quite as good performance as I had before the "event", with ttl RMS error in the .7-.5" range instead of the .5-.3" that I had become used to seeing on most nights.  Part of it I put off to possible seeing issues although PHD2 didn't notice any major star mass changes when I viewed the logs the next day.  The RA spikes

Using the guide scope previously, that is not what I've ever observed in the guiding target.  Switching to an OAG, my hope was I'd see something more like I saw in the PEC recording, but I did realize that with the finer "/PX resolution of my OAG/290MM Mini vs that of the OAG, the movements would appear somewhat larger if everything else were equal.  What bugs me is that I see things occurring with PHD2/monitoring image that I never see while recording the PEC and the PEC recording session was more than long enough for those errant RA movements/spikes to have occurred.  Anyway, the guide performance for most of the session was close to what I had observed before the "event" with periods of guiding TTL RMS error approaching .3".  Which is where I left it for the night.  I was surprised (not pleasantly) when if viewed the PHD2 logs the next day and saw the RA "excursions" and the few quite large RA spikes which had NOT been occurring previously.

Since I've eliminated the external guide scope and all guide imaging is through the primary OTA, and this behavior is not something that showed in the almost full hour of unguided PE recording process, it seems that there must be something I'm doing in the PHD2 tuning etc.  I've been told by numerous other SB users to tune the aggression down as the Paramounts are prone to overreactions with the default PHD2 tuning settings.  I haven't tried it, but one user is sold on using the LowPass2 algorithm on the RA as well as the DEC (I use it on the DEC).  I had used the PPEC with good results on an SW EQ6R and an Ioptron GEM45 mount, but this MyT does not play well with it when I've given it a try in the past.

I'm not a fan of the TSX package when it comes to guiding/imaging/etc. so my primary use of it is as the driver for the mount, PEC corrections, and Tpoint/ProTrack.  I use NINA and PHD2 for the rest of the 'package'.

I've considered that I could be seeing some 'new' indications of RA/DEC mechanical xtalk, and on the suggestions from SB, have reduced the tensions a half turn on the DEC plungers.  It doesn't look like much possibility for any imaging for the next week to test this.  I'm hoping as you review the calibration/guide assistant, and the longer guided sessions that you may see something/have some additional thoughts on tuning settings/algorithms used, etc.

Clayton

PS, to Brian's point, yes the cabling needs some additional dressing up, but the cable to/from the mount pass internally.  The cables to from all the devices (imagers, dew heaters, focuser/rotator) are contained strictly on the mount).  The cables that pass through and leave the mount are just two - the UPBv2 power cable and USB3 comm cable to the same.  Those cables and the Mount power and USB comms go directly to the NUC in the NEMA 4 enclosure you see on the slab behind the pier.
modifying my D-plate mounting setup to see if I can lower the 

[Clayton Yendrey]

One additional bit of info.  All monitoring is via wifi/Remote Desktop from my primary desktop PC in the house.