Guiding "issue"

[Spookyer (Brett)]

Hi all

Just got the big mount and scope (2400mm focal length RC) up on the pier again. Spent most of the day getting the PC ready and the scope and gear ready to go. I am using NINA.
All the usual dramas when setting something up after a break but got through it. Tried some testing tonight. I noted after calibrating in PHD2 and guiding for a bit that the Dec axis is always below the line with all the corrections (red bars) all North. I thought the guiding was consistently pretty good with an error I thought was reasonable but I have never seen this one sided behaviour before. I checked and can’t see a physical reason for it. I did balance the scope on both axis when I set it up and the mount is somewhat forgiving on this anyway.
I have snipped a bit of the guiding graph and it was consistent for over an hour while I did test subs. Any ideas on why this is happening and what I could try to fix it?

[Drac0 (Mark)]

Hi Brett,

Are you sure your PA is correct? I actually had a similar issue last night but both RA & DEC were well off (software issue pointing me the wrong way). I had both running along the -1" line, PHD2 couldn't get it back to centre & I couldn't figure out why. Eventually went back to doing a drift align to get the PA correct & all was well.

Cheers,
Mark

[Startrek (Martin)]

If your polar alignment is poor , particularly in Dec , your PHD2 graph will display typically what your experiencing ( Dec pulses with graph below central line ) Also whilst imaging for an hour or two another tell tail sign is significant Declination drift in one direction left of right. Your object or target can drift a long way left or right after an hour or two
Try to get you PA error below 10 arc minutes or even better down to a few arc minutes.Between 1 and 3 arc minutes is more than adequate for PHD2 to work its magic. As Bruce and Andy have mentioned many times on the PHD2 forum , don’t be obsessive or paranoid about sub arc minute polar alignment, it won’t make you guide any tighter.

Below is a handy PHD2 tutorial on typical guiding scenarios and actions to remedy most issues

https://openphdguiding.org/Analyzing...Guide_Logs.pdf

Hope you resolve this minor issue with your guiding ( your guiding generally looks pretty good )
Thankfully your not experiencing huge spikes in Dec or Ra which is more difficult to pin point

Good Luck

Martin

[Spookyer (Brett)]

Thanks for the replies. I ran guiding assistant after calibrating in PHD2 and it reported a 2.3 arc minute polar alignment error so I didn't actually do a drift align thinking I probably couldn't realistically improve on that anyway.

I did do a 10min sub of the Trifid and it came out rather nicely so it is hard to think the polar alignment is way out but maybe the guiding was in fact just continually compensating for it.

I will run the drift align tool next time and see what it reports. I note NINA has a 3 point polar alignment tool as well that I could try.


Brett