Guiding improves after Meridian Flip?

[WolfieGlos]

I have been using phd2 for guiding for a year now, on the star adventurer and now the HEQ5 since January. It generally runs at an error of between 0.7-0.9” total RMS on the HEQ5. My imaging so far has always been on targets past the meridian, so flips are somewhat new to me since I didn’t want to do them manually on the SA. 

I started off tonight on M63, ran a calibration at 22:30, and imaging about 10 minutes prior to it passing the meridian at 22:58, and the guiding was up near 2” error. Despite this the subs show no sign of trails. But after the flip, it settled at 1.1” and is now down to 0.9 as I type this.. A bit more than usual, but the subs still seem to be OK. 

I’m balanced in RA, so that’s not it. I’m still manually polar aligning but I intend to rectify this later in the year with Sharpcap or polemaster, but would this affect guiding accuracy on different sides of the pier? Is there anything I need to check or consider as to why guiding would be better on one side of the meridian to the other?

Another thought is whether seeing or sky brightness have an effect on the accuracy? When I ran the calibration it was before Astro dark, and M63 was up near the zenith at that point. 

[scotty38]

I sometimes see differences pre and post flip but have always put it down to balance, seeing etc. As long as the guiding is around half the image scale then you'll be fine regardless. Mine is 2.51"/pixel and even when my guiding goes awry and is 1.5 plus I still get roundish stars.

Re your calibration it reads like you did it at the Zenith which you should not do so that might be contributing. If you did it at or near the equator then you can ignore me.

[WolfieGlos]

Thanks scotty, good point about calibration at the zenith...I'd totally forgotten about that. I'll re-calibrate tonight and see what I get.

My image scale is 1.34"/pixel, so the fact the stars looked OK even at 2" I might have got away with it.

[WolfieGlos]

Hmmm, I suspect something else is going on. I’ve recalibrated several times tonight on various stars throughout the sky (not near a pole or the zenith) and I was getting some large jumps particularly in DEC, both before and after another meridian flip tonight.

I was averaging 1.8”, but it has been as high as 3”. Those subs I’ll be scrapping as they show oblong stars 😡

Since then, I’ve restarted the whole session. Parked the mount, re-polar aligned, checked everything is tight, recalibrated phd2…and it’s better but still suffers randomly. It settled at 1.2” but then suddenly I get a spell that goes up to 1.8/1.9”, giving large spikes in the graph in both DEC and RA. Then it’ll settle down again. This isn’t during a dither, but strangely when it has dithered it’s settled immediately. I’ve checked for cable snags and that’s not responsible. The cables hang down to the ground, but are all separated. Any ideas? 

[scotty38]

Sorry only just saw this again. I assume your calibration is completing just fine? Did you try running the guiding assistant and going with its recommendations?

Edited June 5, 2023 by scotty38