Another PHD2 guiding query

[scotty38]

Hi all I'm having guiding issues that I cannot make sense of. All has been well until the last few weeks and now my guiding is very poor and very strange I think. Everything "seems" ok with the mount, balance, no snags etc but of course it can't be but I'm not sure what's wrong due to the issue I'm seeing.

If you look at the graphs below you'll seek ok guiding and then it just goes bad, although the middle one is kicked off by a dither. I "fix" it by stopping and restarting the guiding. Could it be a balance issue and by stopping the guiding I'm allowing the mount to settle as it were, I start again, it eventually oscillates again and rinse repeat. Does that sound like a balance problem or is it likely something else?

[scotty38]

Decided to run another calibration and guiding assistant and hopefully haven't spoken too soon but it's been stable a while.........

[wimvb]

That graph looks like a text book example of an oscillation/resonance. Hopefully, recalubration sorted the issue. You can also try decreasing aggression and increasing minmo.

[scotty38]

1 hour ago, wimvb said:

That graph looks like a text book example of an oscillation/resonance. Hopefully, recalubration sorted the issue. You can also try decreasing aggression and increasing minmo.

I think it did, it ran until dawn and was fine. The eagle-eyed may have spotted min-mo changes that were applied by the guiding assistant along with changes to backlash settings. My last calibration wasn't very long ago which is why I hadn't tried that as I just sort of assumed it would be ok.

I'm not sure what's changed and I've not had to do so before but should I be calibrating each session anyway?

[Stuart1971]

2 hours ago, scotty38 said:

I think it did, it ran until dawn and was fine. The eagle-eyed may have spotted min-mo changes that were applied by the guiding assistant along with changes to backlash settings. My last calibration wasn't very long ago which is why I hadn't tried that as I just sort of assumed it would be ok.

I'm not sure what's changed and I've not had to do so before but should I be calibrating each session anyway?

The idea is that with a good calibration, you don’t need to re do it, unless something changes with your kit or orientation of it, should last for months.. unless it’s ST4 guiding which has to be done with every different object you image.

Maybe it’s the dithering that’s setting off the bad oscillations, if it happens again try a session without the dither, or maybe take a look at the dither settings, they could be a bit aggressive….just a thought. Personally I never dither and have never seen any reason too, unless you don’t use darks, but I prefer to..

[scotty38]

54 minutes ago, Stuart1971 said:

The idea is that with a good calibration, you don’t need to re do it, unless something changes with your kit or orientation of it, should last for months.. unless it’s ST4 guiding which has to be done with every different object you image.

Maybe it’s the dithering that’s setting off the bad oscillations, if it happens again try a session without the dither, or maybe take a look at the dither settings, they could be a bit aggressive….just a thought. Personally I never dither and have never seen any reason too, unless you don’t use darks, but I prefer to..

Thanks but the examples above are with and without dither, just seems that dither was "guaranteed" to set it off....It was fine all night after I recalibrated and I did nothing else whatsoever, in fact I'd done not much more than polar align since the last calibration which is why i was curious as to why it should suddenly not work. I dithered after every frame last night too and not a murmour, just how it usually is. At least I know if it starts like this again then a calibration may fix it although I still don't know why it happens.....

[Stuart1971]

2 minutes ago, scotty38 said:

Thanks but the examples above are with and without dither, just seems that dither was "guaranteed" to set it off....It was fine all night after I recalibrated and I did nothing else whatsoever, in fact I'd done not much more than polar align since the last calibration which is why i was curious as to why it should suddenly not work. I dithered after every frame last night too and not a murmour, just how it usually is. At least I know if it starts like this again then a calibration may fix it although I still don't know why it happens.....

Polar aligning will require a new calibration every time….👍🏼

[scotty38]

1 hour ago, Stuart1971 said:

Polar aligning will require a new calibration every time….👍🏼

Thanks and that’s the answer I need and I guess I must have just been lucky up to this point…..