Any ideas of what is going on here ?
The focus position is the same, the temperature is almost the same, but the hfr increases fast. I am having this behavior in many nights, the focus does not hold in position. Telescope is a FSQ106EDX and the camera asi2600mm. The eletronic focus is the zwo.
Are you using temperature compensation for focusing?
My focus position does not change unless the focuser is asked to do so, but what is interesting is that you are seeing more stars as the HFR increases.
I am using a Sesto Senso2 which ises the Micro Focuser as opposed to ZWO using the main coarse focuser, so not sure about the steps, but I know with my Senso a steps movement of 26 is very little.
Could your focuser be slipping? Is the object high altitude? If so have you tried it on an object where the focuser is not facing downwards?
The places I would focus are
Hope that helps
Simon
Is the target on the west? Targets moving from a higher altitude to a lower one will often see a natural degradation of HFR. That said, I’d think it wouldn’t be quite so pronounced for a shorter FL like this.
Thanks STAstro, your response helps me to think obejctively on the matter.
a) I am not using temperature compensation. 26 steps is very little, but noticiable with a bathnov mask for example. The autos focus routine works very precisely and consistently, always given the same postion, more or less 3 steps. What I am trying to avoid is to run autofocus at each 6 frames, what I need to do now if I want the best focus through out the whole night.
b) I can rule out dew, because image is clean, good feating, and I always have good HFR when refocus
c) My setup is almost always pointing high altitude, since I dont image below 45 degress if possible.
At this point most probable I am having a focuser slip, just by a tiny amount. It is a good ideia to test in a low altitude object. thanks
This target was on the west, going lower altitude but it happens on the other side of the meridian too. I have to admit it must be a mechanical problem. Which is problematic since I am 300km alway from my setup to check, and not planning to go there in the next weeks.
one question remains unanswered to me: why the number of stars increases with the HFR ? Maybe the 3nm halpha filter have something to do with it ?
If you are referring to more stars showing up in the autofocus routine as it gets more in focus, that’s normal. A star can be defocused to the point where it’s not recognized, but as it becomes focused, it’s picked up by the AF routine
Brian
I guess he referred to the data in the screen shot shown in the first post of this thread: at constant focus position, while the HFR value increased from frame 3 to frame 12, the number of detected stars increased as well.
Bernd
It could be because more stars are coming into focus that it is using a wider set of stars, and some of those stars could be bigger and thus increasing the average, hard to say really without being able to see the frames
For the first time EVER I just checked my image history, not much in the way of thermal expansion and contraction on my scope, last night temp was 11.8C and tonight it is 15.3C and there is only 4 steps difference, and that’s 4 steps on the micro-focuser with the Sesto Senso 
Hi,
Have you considered that star detections and HFR values might also change as a result of factors other than temperature change and focuser movement? In particular I am thinking of deteriorating seeing resulting from e.g. arrival of thin, high level cloud.
I would take a look at the median background levels of what you consider the ‘well-’ and ‘poorly-’ focused images. If there is significant change in these values then I suggest the HFR and star detections deltas you are seeing may well be due to deterioration in local seeing, not of focuser slippage, poor response to temperature change or AF software gremlins.
Regards
Mike
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