Bizarre Ekos guiding issue after meridian flip

[AstroViking (Steve)]

Hi all,

I had the scope out last night to take advantage of the first clear night in about a month.

My target was IC4628, the "Prawn Nebula" because it's a good Ha target and one that I haven't imaged before.

For the first half, I was seeing a guiding RMS between 1.5 and 2 - all well and good. The guiding graph was pretty much flat, and when I checked the subs the stars were good and round, even in the corners of the image.

The meridian flip went smoothly - Ekos re-aligned with the Prawn, the guiding started up after recalibrating, and then it all went stupid.

Instead of an RMS in the single figures, it was sitting at 30. The stars in the first couple of images were all good and round, so I left it running. When I went back to check, Ekos had aborted the sequence because the guiding RMS was (obviously) well above the threshold.

At this stage I gave up and packed everything away.

It's not the first time I've had this situation, yet other times the flip happens and everything works perfectly afterwards.

So my questions:

- What is causing the insane guiding RMS values, when all that's happened is the meridian flip?

- What can I do to resolve this? (Besides doing a full power-down and restart after the flip?)

Many thanks,
V

[oska (John)]

Assuming it's not mechanical cables, stiction, etc. and not clouds or headlights or torch or the like zapping it (I had a BIG rhino beetle crawl over it once) there is a setting 'Reverse Dec output after meridian flip' that, at least in phd2, can magically be off occasionally. Whenever I see what you're seeing and it's not cables, it's that config switch that is to blame. I know ekos has it's own guide module but the symptoms are the same.

[RugbyRene (Rene)]

Hi Steve,

I feel your pain. I've had the same thing happen to me. Guiding East of the Meridian at 0.7-.08 RMS, then the flip and it all goes to crazy.

I don't know if it's a flaw with KStars or something with the mount but I haven't been able to figure it out. I've had a few weird things happen with KStars which has made me consider switching to NINA. But maybe that's has the same quirks.

Rene

[Drac0 (Mark)]

Originally Posted by oska

there is a setting 'Reverse Dec output after meridian flip' that, at least in phd2, can magically be off occasionally. Whenever I see what you're seeing and it's not cables, it's that config switch that is to blame. I know ekos has it's own guide module but the symptoms are the same.

Hi John,

Will have to check this out as it's not enabled by default in PHD2. They explain well how to test it, so will do that next chance I get - my guiding always seem much worse after a flip.

EDIT: Just noticed PHD2 has a "wizard" to test this under the Tools menu. That will make it easier to test & see if the reverse dec is needed..

Thanks,
Mark

[AstroViking (Steve)]

Hi all,

I've done some more research since my original post, and I'm not alone in having this problem surface.

It seems to be intermittent, as I did not have this problem when I imaged the Dragons. I am wondering if it's because I balanced the mount slightly east-heavy this time?

I'll see what happens next time I get a clear night...

Cheers all,
V

[oska (John)]

Originally Posted by Drac0

Hi John,

Will have to check this out as it's not enabled by default in PHD2. They explain well how to test it, so will do that next chance I get - my guiding always seem much worse after a flip.

EDIT: Just noticed PHD2 has a "wizard" to test this under the Tools menu. That will make it easier to test & see if the reverse dec is needed..

Thanks,
Mark

I should have included this was only for sky watcher mounts and GSS, my Ioptron and Losmandy don't need the switch.

[AstroViking (Steve)]

Hey all,

I just remembered that Ekos can interface with PHD2 for guiding, rather than keeping with it's internal guiding module.

I'll have a go at getting PHD2 up and running and see if that makes any difference.

Have a great weekend!
V.

[AstroViking (Steve)]

Evening all,

Well, the mystery gets deeper.

The Ekos built-in guide module is working perfectly after the meridian flip. I was getting an RMS of under 1 arc-second before the flip, then an RMS of just over 1 arc-second afterwards.

I'm beginning to think that there's a grumpy spirit living in my mount and I've done something to appease it...

Cheers all,
V

FWIW - I did install and configure PHD2 and was going to use it but thought I'd give Ekos another try, seeing it's only a short session tonight.

[AstroViking (Steve)]

Hey all,

Interesting - the rig is out and imaging right now. I got about 1 arc-second RMS guiding before the flip, and am getting about the same afterwards. (Yes, doing OSC imaging under a full moon!)

The only thing I can think of that's likely to cause guiding issues is the way I balanced the scope. The last 2 sessions I have not set it to be east-heavy (ie, counterweight-heavy) and the guiding has been perfect.

Given the HEQ5 has the belt-mod done to it (and has effectively zero backlash aside from the worm-drive to brass cylinder-gear) would balancing the rig to be counterweight-heavy cause guiding problems?

Cheers,
V

[AstroViking (Steve)]

Just to further expand on this - I balanced the mount equally on both axes. No counter-weight (East) heavy and got an average of 1 arc-second guiding all night long before and after the meridian flip.

Looks like it's going to be an evenly balanced mount for me from here on.

Cheers,
V.