Voyager & PHD2 Calibration

[Elusive Photons]

If using Voyager for automation and PHD2 for guiding, PHD2 always complains about calibration location.  (Popup Error)  It is easily dismissed but annoying because it happens every time.  Voyager does not calibrate at the meridian it calibrates close to the target you are imaging.  This is not something that is able to be changed and from what I've read on the Voyager forums, the developer is not interested in changing.  (He believes his way is the best way)

Can we get an option to disable this message or 'check' permanently?

Thanks!

[Elusive Photons]

Sorry, I meant Declination Zero not 'meridian'.   Thanks

[Bruce Waddington]

I don't know what "popup error" you're talking about so you need to take a screen-shot of the message along with the associated guide and debug log files.  Upload those log files using the built-in 'Upload Logs' feature in PHD2:

https://openphdguiding.org/getting-help/

I also don't understand why you're doing so many calibrations in an environment where a session manager app is controlling things.  The reason we discourage calibrations being done at high Dec values is based on mathematics, it's not just some random notion.  We have other Voyager users who also use PHD2 and they have haven't registered this complaint, so I think your choices of operational procedures have probably put you in this position.

Bruce

[Elusive Photons]

Hi Bruce,

I will grab a screenshot my next available opportunity.  The message pops up once guiding starts and says something like 'Calibration was done too far from the equator, re-calibration required'

In Voyager you select calibration in the sequence and it performs it at the beginning of the imaging session at the DEC matching your target and after a meridian flip.  So it only does one or two calibrations per night but the error pops up every time guiding stops and restarts.  (ie. after an auto-focus run)

More info here: https://forum.starkeeper.it/t/possible-to-define-guide-calibration-location/5159

Some more info here: https://forum.starkeeper.it/t/guider-calibration-and-camera-questions/508

Is it bad to calibrate at the DEC of your target?  PHD2 seems to run fine when doing so...

Thanks,

Craig

[Bruce Waddington]

You ask "is it bad to calibrate at the Dec of your target?"  I would say it ranges from being sub-optimal to bad to hopeless as you get closer to the celestial pole.  You have to think about what's going on and how the spherical geometry of the night sky affects calibration.  Let's suppose there was a star exactly at the north celestial pole and we tried to calibrate on that star.  The calibration would fail completely, guaranteed.  Why?  Because the guide star would never move as we issued guide commands in RA no matter how long we let the calibration run.  So what happens if we move a short distance away from that singularity?  Then the RA guide commands will cause the star to move but only by very tiny amounts.  Now we would be trying to measure very tiny movements in a sea of other disruptive effects - the guide star is bouncing around from seeing, the Dec is drifting because of polar alignment error, the payload gear is shifting around due to flexure or wind, and the sidereal tracking of the mount is varying because of periodic error.  In the aggregate, all of these are likely to be larger than the tiny movements in RA that we're trying to measure.  So now we can extrapolate and understand that the further we move away from the celestial pole to do a calibration, the better we are able to measure the RA movements we're interested in - the ones coming from the RA guide commands - and not get lost in all the other unwanted "noise".  This is why we push people to calibrate as close to Dec=0 as their site conditions will allow.  A good calibration there will be the most accurate measure of how the mount responds to guide commands and that accuracy can be leveraged at any other pointing position in the sky.

If you have a permanent setup, there is no reason to re-do calibrations unless you make changes to the orientation of the guide camera or change the guider image scale.  For example, I have a permanent remote observatory setup and my last calibration was in March 2024, and the only reason for that is that I was testing the Calibration Assistant.  If you have to set up and tear down your gear every night, the sensible thing is to do a single calibration at the start of the night, probably during astronomical twilight when you're not ready to image anyway.  Don't let the session manager app do it, do it yourself from the keyboard using the Calibration Assistant and remove all the calibration directives in your session manager plan.   I think the approach you're using now is a waste of time at best and degrades the ability of PHD2 to produce the best possible results.

Regards,

Bruce