PHD2 fails to calibrate after meridian flip

[Richard Thomas]

Hi all,

Until now, I used to calibrate my guiding before an imaging session and never again. The ccalibration procedure runs just fine and I get good guiding, until I perform a meridian flip. I found that guiding got worse, so I decided to force a calibration after a meridian flip in NINA.

Unfortunately, I found out this morning that the calibration didn't work. It performed two West steps which I think pushed the stars out of the field of view and resulted in the calibration failure. See the ZIP file below which contains guide logs and debug logs along with the critical times when an event took place.

https://openphdguiding.org/logs/dl/PHD2_logs_Grt5.zip

Critical timings:

2022-08-11 22:06:52 -> Original calibration at start of session

2022-08-12 00:44:55 -> Stop guiding ahead of meridian flip

2022-08-12 01:01:19 -> Perform meridian flip (NINA log)

2022-08-12 01:09:33 -> Begin new calibration after meridian flip

Mount is an EQ6-R. Within PHD2 guide settings tab "Reverse dec output after meridian flip" is unticked. Please could someone let me know what caused the calibration after meridian flip to fail and how I can rectify.

Cheers,

Richard

[mj.w...@gmail.com]

Hi Richard

Before the experts unravel this, I would point out your guide rates are very low:

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

This is usually due to leaving the EQMOD "ASCOM PulseGuide Settings" on the default:

Michael

Wiltshire UK

[Brian Valente]

Have you tried using the calibrate meridian flip tool? under Tools menu

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Brian 

Brian Valente

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[bw_m...@earthlink.net]

Hi Richard.  I think you need to go back to the original problem, which is why the guiding got worse after a meridian flip.  Looking at the calibration failure, it looks like the mount behaved very badly with the first “west” calibration step after the meridian flip, moving so far that the guide star was lost.  I think you need to trouble-shoot this manually, not running NINA and not trying to do an automated imaging session.  As Michael said, you should first fix the guide speeds in EQMOD which are absurdly low – I’m surprised you were able to get anything done with these settings.  Get the mount guide speed settings up above 0.5x sidereal.  Then create a new PHD2 profile using the new-profile-wizard and specifying the correct guide speed.  None of this will fix the current problem but it will help get things back where they should be from a software perspective. 

 

Once you’ve done this and gotten a reasonable calibration,  you should position the scope on the west side of the pier, pointing at Dec = 44 degrees.  Then force a meridian flip so the scope is on the east side of the pier still pointing at Dec = 44.  Look very, very carefully to see if there are cables binding or pulling, anything that interferes with the ability of the mount to move smoothly. With such slow guide speeds, the setup was especially vulnerable to these things.  I think cable routing is the most likely source of the problem, those issues often show up after a meridian flip.  Don’t start fooling around with software settings like “Reverse Dec output”, those have nothing to do with the problem and will just take you down a blind alley.

 

Good luck,

Bruce

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[Richard Thomas]

Hi all,

Thanks for the tips and advice. I was able to try a few things out last night and I think I understand where the problem lies. Let's cover your suggestions below.

• Cables aren't an issue. The only ones which dangle are the EQDIR and 12V power cable, but they are long enough to not snag, bind etc.
• I've now updated Guide rate for RA and DEC in EQMOD to x0.50 and created a new PHD2 profile
• I tried the Meridian calibrate tool which highlighted an issue
  • WEST side of pier calibration worked fine
  • EAST side of pier calibration would not slew back to required coordinates (RA = meridian and DEC = 0 degrees). I had to disable mount limits to complete the slew and calibration worked fine
  • Note: I have set up mount limits to avoid collision between my imaging camera and tripod legs
    

Attached are my guide log text file from last night. Here are the key events at the stated times:

23:38:48 -> Part 1 of Calibrate Meridian Flip - WEST side of pier

23:47:01 -> Part 2 of Calibrate Meridian Flip - EAST side of pier

23:50:00 -> Slewed to NGC7000 which was at Meridian. Flip was performed.

23:52:19 to 01:22:36 -> Failed to slew back to NGC7000 after meridian flip (the furthest East it would slew was to IC 5070 Pelican nebula)

01:25:12 -> Aborted NGC7000, slewed to different target (Sh2-171) and commenced guiding and imaging

04:09:01 -> PHD2 attempted recalibration which failed, due to loss of stars as dawn approached

It looks like after the meridian, EQMOD was preventing the telescope from slewing back to NGC7000 due to the mount limits I set up. The default limits are at RA 0 and 12, but I'm sure mine were slightly wider than that. However, if I have set the EAST side to be slightly tighter, that may explain why I can't slew towards the meridian after the flip has occurred which would further explain why the forced calibration in my original post failed. This seems concurrent with what I experienced during the Calibrate Meridian Flip tool per above.

I'll double check my mount limits to see if it's an issue. FYI, I aborted NGC7000 at 1:25am as I needed sleep, so I set up an imaging run for Sh2-171 (doesn't require meridian flip just yet!) which went perfectly fine without issue.

Thanks for your quick responses and good suggestions :)

Cheers,

Richard