EQMOD pulse guiding and RA width gain

[swag72]

Last night I was running 20 minute subs and the guiding was OK. When I say OK, I mean that the guiding graph was jumping all over the place ( there was a lot of humidity) but the subs are fine and show no problems at all.

I had a quick look at the EQMOD pulse guide graph and noticed that the RA axis was particularly awful, showing massive and consistent saw teeth as I have highlighted in the attached. The guise says that in this instance the RA axis is over correcting and that I need to lower the RA width gain settings. But ............ the stars in the subs were fine.

Should I be seeing some awful guding and star shapes with this issue? I'm not looking for problems ..... honest!!! More of a wonder really.

And I am guiding using Maxim, so would reducing the aggressiveness have the same effect?

[chrisshillito]

Should I be seeing some awful guding and star shapes with this issue? I'm not looking for problems ..... honest!!! More of a wonder really.

And I am guiding using Maxim, so would reducing the aggressiveness have the same effect?

The graph is telling you that the autoguider is apparently over correcting - of course it could be that the corrections are very small and the over correction is a result of the EQMOD being unable to accurately produce the requested pulse. Whilst sawtoothing may give the appearance that something is wrong , it does still represent control, and won't necessarily spoil your subs if the movement the oscillation produces is sub-pixel. Ultimately the proof of any guiding is in the subs you obtain - not the guiding graphs. EQMOD's graphs were introduced to help diagnose guiding problems - if you don't have a problem then I wouldn't worry to0 much about them

I don't use Maxim so can't comment with any authority on what effect reducing aggressiveness would have. The gain setting in EQMOD acts to reduce the period of the guide pulses thereby producing less movement at the mount for any observed movement of the guide star. Maxim's "aggressiveness" setting may do the same kind of thing but its behaviour may also be interlinked to with other guiding parameters (hysteresis, minimum motion etc.).

Chris.

[swag72]

Excellent, thanks for popping in Chris. I was quite surprised when I saw the graph and even more surprised when I saw that the subs were OK!!

I may have a little tinker tonight - What's the minimum sort of value I'd be looking at putting the width gain settings to?

[chrisshillito]

Oh well you know guiding, you just fiddle with the settings until it feel right .

Ultimately Maxim should have learnt the response of the guiding system when it calibrated (I assume it has a step equivalent of PHD's calibration) and so you wouldn't expect its guiding pulses to be too far off what is required. I'd just nudge the gain down 10% at a time until it smooths out a bit and check that the subs are still looking good. Of course if you go too far you will get an under correction and start seeing a downward staircase like trace such as that labeled (5) on the diagram (or its inverse).

Chris.