ZWO EFW36 vibration during filter change cause guide issue

Sembra piu’ un problema di connessione tra le parti che altro. Cambiare filtro in una ruota implica sempre una coppia applicata fuori asse, ergo in particolari configurazioni questo puo’ dar luogo alle “vibrazioni” suddette.

You’re not by chance using an OAG? or do you have filter offsets programmed?

I did a test the other night and was very surprised by the results.

If I start the guide in "preview" mode (Asiair), if I then manually change the filter in the EFW36 wheel, the guide doesn't notice.

I've done several tests, and I'm sure of this.

If, on the other hand, I set a session to autorun, the classic L>R>G>B without focusing (I use the offset), the guide peaks when I change the filter.

It's incredible.

So as andrea was eluding to, the spike is because you are not pausing between filter changes.

The reason you ‘sometimes’ see it and sometime dont, is because of focuser backlash compensation. If your focuser moves in the direction under tension, the star size changes very minimally and you may not even notice in PHD. However if your offset shifts focus in the direction of backlash comp, you’re seeing a large jump in focus. This is the spike you are seeing.

It’s recommended to disable guiding during filter change.

Feel free to start your preview mode, do the guiding again. Shift to a filter, THEN shift back to the previous filter. You should see it then.

I wouldn’t be surprised if a recent release for the ASIair messed something up. I’ve been seeing a few strange, unexplainable occurrences in the past few days from asiair folks. And they all seem to be interactions with PHD2

if you’re using filter offsets and an OAG, chances are your spike in guiding is caused by the focuser movement (potentially focuser shift, but more likely focuser backlash compensation or abrupt movement), not the filter change…

You can tell most imaging software to pause guiding during a filter change, that will probably resolve the issue regardless of the cause.

Also, when you say the OAG is after the filterwheel… Do you mean you’ve got:
Telescope → Filter wheel → OAG → Camera?

If so, when the filterwheel rotates, there will be a brief moment where the signal on the guide stars is cut off by the carousel, this will cause a marked drop in star snr, which could account for it too.

You ‘should’ be running:
Telescope → OAG → Filter Wheel → Camera.

Furthermore, a dither will cause some disruption in guiding, as you’re physically bumping the mount slightly to achieve the dither, there is always a period where the mount settles, your guiding and imaging software should be waiting for guiding to settle before commencing imaging.

Lastly…
Dithering between L → R, R → G, G → B is 100% overkill. These frames are not stacked together, they are combined into individual stacks. Therefore, the accepted norm is to shoot L, R, G, B → Dither. That way, you’re dithering every frame PER STACK..

I personally shoot L L L R G B → Dither, I find that 1 dither per every 3 L frames is plenty (given the exposures are half the duration of a R G or B frame also).