Option box to recalibrate PHD2 after Meridian flip

Hi I’m having a great deal of trouble with my calibration after Meridian flip. I think this has to do with multiple issues including the difference in weight distribution on one side of the pier versus the other. Obviously there are many things that I could try to make sure that this is all working but it would be much easier to just have sequence generator pro request recalibration after Meridian Flip. I’m very frustrated when I set out to photograph an object for eight hours during the night and find that it’s only completed half when it was interrupted by a autoguider that wasn’t settling postmeridian flip.
Regards and thanks for making astrophotography and sleep compatible.

Most of the time problems with PHD2 guiding after the meridian flip are related to the Reverse Dec Output after meridian flip setting.
The correct setting for various types of mounts is available here: https://github.com/OpenPHDGuiding/phd2/wiki/Reverse-Dec-output-after-meridian-flip
If your mount is not listed or if you want to confirm the setting, PHD2 can automatically determine the correct setting for you: https://openphdguiding.org/manual/?section=Tools.htm#pierflip_cal_tool
Feel free to post in the PHD2 forum if you need any help with it.

Hi Andy

Thanks for your prompt reply, your team are the GOAT.

I use EQMOD and have not reversed Dec settings in the past. My problem is my mount setup does not have the same backlash on the East side of the mount as it does on the west. It would be good to recalibrate but certainly I will keep at the task of trying different PHD2 settings.

Again, appreciated.

Jim A

Jim, That’s not uncommon, but recalibrating shouldn’t make any difference in that regard since calibration measures the camera angle and the rate of the guide pulses, and neither of those are affected by backlash. When the mount does a pier flip, the camera rotates by 180 degrees and the guide rates are unchanged.
We can take a look at your guide log to see what the problem was after the meridian flip and confirm whether or not recalibration is the right solution.

Is this what you are after. I select this option to carry out a re-calibration PHD2 after a Meridiam Flip.

Also this option needs to be disabled

Hi Robin

This does not cause a recalibration as it is the same target.

But yes if this box said recalibrate after meridian flip or new target it would do the job.

Thanks for you continuing efgorts.


This option does relate to a new Target, but if a flip takes place then a re-calibrate will happen as well even if its the same target.
This is how I get Mine to re-calibrate after a flip.
I agree, maybe there should be an option just for Flip/Re-calibration…

Hi Robin

I have not seen it recalibrate after a flip but then again it usually flips while I am asleep. I don’t think my PhD2 log has shown a recalibration after a flip. Does yours. Anyway it is your software so you would know better than I. I am away for a few weeks (in Italy) so will not be able to test it.



Hi Jim,

Finally, I was able to find some time and clear weather, to do a retest of the ‘re-calibrate after a flip’.

I have to say you are correct on the flip PHD does not do a re-calibrate. Now it use to calibrate in earlier versions of SGPro. I know this for a fact as I have watched it on many occasions do a Calibration without any intervention of the user after a flip.
So in the past for some reason, if a flip had taken place it was on a new target even though it was the same, which I found very handy as it was a work around for this problem.

So something has changed either in PHD or SGPro which prevents this work around from working any more. So I guess whats going on, if a flip takes place, it automatically flips calibration data. which great I guess but doesn’t work on my mount to well so it’s not reliable.

This would explain why my guiding had started to become a little erratic, and having to do a manual calibrate to fix the problem.
I just assumed something else was causing the issue and never thought to recheck if the calibration was still happening after flip until you mentioned it.

So there should be an option in SGPro to allow users to make a choice whether to auto calibrate or not after a flip.


Hello Robin

I am thrilled at the prospect of the modification to SGPro that will make my astrophotograhy more reliable and satisfying going forward and I suspect you are too. I am very impressed by the investigation you did and your open mindedness (which is rare in the product world when faced with customer suggestions/complaints).

I hope the modification does not require too much work on your part and am glad it will benefit you too.

Btw I am in the process of building a new robotic observatory at a site with clearer skies than my inner suburban one Melbourne and this would be much harder without SGPro(so very gratefull). I love this hobby particularly the technical side and automation which gives me as much if not more satisfaction( getting it to work) as looking at the final pictures themselves.

Please let me know when the mod will go live.



Hello Robin
I am sorry for assuming you were part of the development team. I understand you are a member( Like me) so it is not your responsibility. Still gratefull you were able to corroborate my findings. I hope Andy and the team at SGPro agree a modification is necessary.

Why is a recalibrate needed after a meridian flip? The flip can change the sign of some of the corrections but there’s no obvious reason why the calibration, in terms of guide correction size required for a guide star error should change and that’s all that the calibraton will change.

It may be useful to try doing a calibration for the same object before and after a flip and see what changes. This wouldshow what changes. Maybe it is possibe to configure the way that PHD behaves after a flip so that a recalibrate in not needed.

1 Like