Recommended settings for my mount as well as reverse dec problem

[Aidan Bonicker]

Hello,

I have a Star Adventurer GTI mount that I've been having RA problems. I had it sent to Sky Watcher and they said it was perfectly fine. Since then I've been throwing out a lot of my photos depending on the night. A few nights ago I did an unguided test for 100 minutes near the celestial equator and I've attached the log if someone could take a look. 

Later that night I used PPEC for my RA and it worked decently only having to throw away 20-30 percent of my subs. Tonight however was the opposite and every sub was trailed. I decided to switch to Hysterisis and this seemed to calm things down. What I'm unsure of now is whether it was Hysterisis that fixed the problem or if the meridian flip is what fixed it because I changed them at the same time.

Another issue that's started recently is after meridian flips my DEC corrections send it the wrong direction. I've tried turning on and off reverse dec in the settings, but its either not letting me do it or its not working. The reason I say its not letting me is that when I stop guiding, enable reverse dec and resume guiding, it opens up the calibration assistant and I have to restore calibration. Not sure if me switching it on and off is even doing anything because it keeps forgetting the calibration when I press it. This is a lot of stuff, but I would appreciate the help because Sky Watcher has been useless so far.

Thanks, Aidan

[Michael Waring]

Hi Aidan

You need to follow the instructions at the top of the home page "How to ask for help with PHD2"

That uploads the Guide and Debug logs.

[Aidan Bonicker]

My mistake. I forgot there was a specific way to upload. https://openphdguiding.org/logs/dl/PHD2_logs_Hmon.zip

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[Bruce Waddington]

Hi Aidan.  We can start by considering your problems with Dec reversal after a meridian flip.  Here's the explanation of that setting from the User Guide:

'Reverse Dec output after meridian flip' -  tells PHD2 how to adjust the calibration data after a meridian flip.  Some newer mounts track their 'side of pier' state and automatically reverse the direction of the declination motor after a meridian flip.  Older mounts do not do this.  In either case, PHD2 needs to know if the mount will automatically change its behavior based on side-of-pier.  You may have difficulty finding information about how your mount behaves in this respect, so PHD2 provides the Meridian flip calibration tool to determine the correct setting automatically. It's also easy to figure out the setting manually with this quick experiment:

    With the checkbox disabled, calibrate on one side of the pier, then move the mount to the other side.
    If you are guiding via ASCOM or Indi or are using an 'aux mount' connection, just start guiding.
    If you're guiding only via ST-4 and PHD2 has no scope pointing information, first select 'Flip Calibration' under the  'Tools' menu, and then start guiding.
    In either case, if the guiding works normally, leave the box un-checked; but
    If you see guiding run-away in declination, check the box and repeat the entire procedure, including calibration.  You         must repeat the procedure, simply checking the box doesn't "fix" anything.

Note: this procedure must be following in its entirety until you determine the correct setting.  Changing the 'Reverse Dec' setting only determines what will happen in the future, at the next calibration.

So we implemented a tool for you to get this sorted out in the event you got wound around the axle (which you probably did).  And PHD2 isn't "forgetting" your calibration, it is trying to force a new calibration because you changed the setting. If you are then literally restoring an older calibration, you're just shooting yourself in the foot.  Bottom line, your mount almost certainly needs to have the 'Reverse' option checked - so check that box, re-calibrate, and you should be good to go with Dec corrections and meridian flipping.  Also, don't start fiddling around with Dec guide mode being turned off or setting it to uni-directional, leave it alone on 'auto' until you get clear evidence that your mount has too much backlash in Declination.

In terms of your problems with high rates of star elongation, I don't think you've given us enough context to help.  Elongated stars can come from source that have nothing to do with guiding or even mount tracking.  For example, the 2.5 hour long guiding session you started shortly after midnight produced RA and Dec RMS values that were pretty close.  Granted, the total guiding RMS was almost 2 arc-sec but that, alone, won't normally produce elongated stars.  What is the image scale on your main camera?  How long are the main camera exposures?  What is the total weight of the payload riding on the mount?  Can you post a photo showing an overall view of the mount, the payload on the mount, and cabling?  

As you probably know the periodic error on your mount is very high with a periodic error over 50 arc-sec peak-peak:

The question is whether Sky Watcher thinks this is "perfectly fine".  I can't say because this is an economy mount in the grand scheme of things and I don't see anything in the specs that talks about periodic error. So  I would say your expectations should be pretty modest with this mount - usually meaning a very light payload and relative short exposure times with the main camera.  By the way, PHD2 guiding managed to wrestle this periodic error down to less that 2 arc-sec peak-peak.  If you want to help PPEC further improve on this, you should find the PPEC settings on the Algorithm tab of Advanced Settings and set the period length to 480 seconds and un-check the box for "Auto-adjust periodic length".  Also, increase the predictive weight to 80.

If you intend to get into an extended period of trying to get more from the mount, you should start by following the attached procedure for get a measurement baseline of its performance.  You should also update to the current 2.6.14 release of PHD2.

Good luck,

Bruce

[Aidan Bonicker]

Hi Bruce,

I ended up finding the meridian flip tool last night and that sorted everything out.. My image scale is 1.63 arc seconds per pixel so not too zoomed in. My overall rig weight is 7.8 pounds which is under the 11 pound capacity, but some may say that's pushing it. I have seen countless examples however of people putting 11 or 12 pounds on it and they get 0.5 rms.

I was taking 5 minute sub exposures, but I've knocked this down to 3 minutes to reduce the chances of something going wrong. I've attached photos of before and after the meridian flip and change to hysteresis.  As for the PHD2 update I am unsure of how to update it through stellarmate. What I've seen online says that PHD2 should just update when the stellarmate software updates, but my software is fully up to date and I'm not sure how to install the updated version through linux.

A little more detail to my skywatcher story. They had me send my mount all the way to California where they did some kind of test on it with an artificial star I believe. They sent me an email back saying it performed up to standard. I replied asking if they could double check the RA clutch and maybe do a regreasing, but they ignored me. They sent me another email saying they will begin the process of sending it back soon, I replied again copying and pasting my old email and they ignored that too. It's been pretty frustrating. I also agree that 50 arc second peak to peak is very high, but I haven't found anyone else sharing their mount error so maybe it's normal.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/ce8f3cc5-f276-4a65-9e29-4eb032beafc6n%40googlegroups.com.

[Aidan Bonicker]

Hey Bruce,

I have some additional info I think I just confirmed from tonight's imaging session. It was in fact the meridian flip that fixed my guiding. I couldn't get a single good sub for 4 hours and after the meridian flip is when it finally got better. I let  PPEC and Hysteresis run and both were bad. https://openphdguiding.org/logs/dl/PHD2_logs_4fF3.zip

 This is a link to last night's guiding which I think may be more useful because I left the mount untouched for most of the night before and after the flip. Tonight I was tweaking settings every few minutes and I don't think it would be very useful. Both nights should be very similar though.

I don't really see how this problem can be caused by anything but a mechanical issue, but I guess i'll see what you think.

On Fri, Jul 3, 2026 at 10:18 PM Bruce Waddington <bw_m...@earthlink.net> wrote:

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/ce8f3cc5-f276-4a65-9e29-4eb032beafc6n%40googlegroups.com.

[Brian Valente]

Hi Aidan

Twoquestions to start:

Can you send a few pics of your imaging setup?

What is the image scale for your imaging setup (arcseconds per pixel). Or at least what is your imaging telescope and camera.

From this last guidelog, it looks to me like you were fiddling with settings pretty much all night until your last sessions. That must have been frustrating.

Before the flip, you never really got an acceptable calibration, so the results were predictably not great. You also fiddled a lot with Dec by disabling it, or guiding in only one direction. That ended up working against you and there were some runs where RA was okay but Dec was uncorrected.

If you find you need to guide Dec in only one direction, take a look at the section in the manual on how to set that up so you get the best results: https://openphdguiding.org/man/Supplemental_Info.htm#Declination-Uni-directional_guiding 

In RA, generally speaking not much has changed. The primary period remains very high around 40" peak-peak and is the constraint to your guiding. PHD is doing a good job guiding it, but the residual (uncorrected) is still 2". That may or may not be acceptable in your images, depending on the image scale (see first question above). 

I think your best approach may be to use more aggressive RA guiding with a faster exposure time of maybe 1.5-2 seconds and higher aggression.  You can try PPEC but your aggression will need to be much higher, i would go for 90 in both predictive and control gains. 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAKVYnaAtZXsVp3bf3S_26pebrVXFVkhX0JpnmjzvET5ZFktFHg%40mail.gmail.com.

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Brian 

Brian Valente

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

[Aidan Bonicker]

 

Hello Brian,

I've attached two pictures of my rig.I have had the stellarmate attached to the scope before instead of strapped to the pier extension and these RA problems have happened either way. I still have the wires fairly well organized. The reason I do this is because I don't have an easy way to attach my stellarmate to the rig and I also have a lens setup that I use sometimes, so having the stellarmate on the pier makes it easier to setup the lens. The scopes focal length is 360mm so that paired with my camera is 1.63 arc seconds per pixel

Yes this has been incredibly frustrating. Nearly every clear night the past month has been spent trying to deal with bad guiding for hours. The other night I don't really know the reason, but my calibration was having problems. I think the last one was considered ok from PHD2 though

Some other behaviors I've noticed is that when plate solving and slewing to my target just taking 5 second subs and having a 10 second settle time, the stars will trail frequently. There is a definite settling problem with the mount as also seen in my logs with the 'failing to settle after dithering' and that's with a 25 second settle time. Also recently I can't do 3 point polar align. I don't get consistent numbers run to run so its basically useless. I don't really need to do the alignment though because the polar scope on the mount gets me really accurate already, around 1 to 5 arc seconds.

I was able to fix the Dec problem I was having with the meridian flip tool and also Bruce mentioned it to me.

Thanks, Aidan

[Bruce Waddington]

I don't think we're really making any progress here.  It's clear that these are mechanical problems but they have nothing to do with PHD2 settings.  PHD2 is just the bearer of the bad news. The question is where the mechanical problems are coming from.  It sounds like your interaction with SkyWatcher was probably pretty generic and if the major point was that you are getting elongated stars, that's not likely to get any traction with them.  So one thing you could do is put the graph of the unguided RA tracking in front of them and ask 'is this really what you expect from this mount?'  That is at least a specific question.  That said, I really have suspicions about your setup now that we have a couple of pictures.  You haven't provided us with the specific product identifiers for all the stuff you have riding on the mount, but I suspect it's overloaded.  The rated capacity of economy mounts is typically for visual use, meaning that the mount is basically capable of slewing and tracking sufficiently well for visual observing.  Auto-guiding is much more demanding than that. Unless the manufacturer says otherwise, the rule of thumb for imaging is usually to discount the stated capacity by 30-50%.  And the payload question isn't just about the total mass, it's about how that mass is distributed.  In your case, you have a rather "long" assembly, it's not a compact mass that sits right over the center of mass of the mount.  This affects the mechanics because it creates higher moments of inertia and can place more demand on the bearings.  I notice that the counterweight seems to be clinging to the very end of the Declination shaft - is the payload completely balanced in RA at this point or is it simply the best you could do with the current constraints?  I think the only way you could resolve this question is to temporarily mount only the guide scope and guide camera to the mount - the absolute bare essentials, none of this other stuff.  Then run PHD2 manually and get measurements of the uncorrected RA tracking and then the guiding performance near Dec=0.  If it's just as bad as before, then you know it's the mount and you'll have to then decide how you want to proceed.

Cheers,

Bruce

[Aidan Bonicker]

Hey Bruce,

I agree that there probably isn't much more you can do. Thank you very much for your time and ruling out that my issues weren't in phd2. Also just to add on, I have used my samyang 135mm  lens with my touptek camera on this mount which is a much lighter and not as long of a setup. Guiding was basically just as bad so it seems like a mechanical issue and not being overcapacity

Thanks again, Aidan

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