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Thanks mate :-)
Well, the M83 L stack was about 1.8" FWHM and this one was 2.3" Wasn't just seeing though, SGP wasn't doing a great job with focus on this target. I also hit this with decon and sharpening to and mitigate it.
I'm still not sure what the cause of the elongation is, since it didn't really manifest much with M83. I suspect astigmatism, possibly due to secondary collimation, which only manifests as elongation when the focus isn't perfect.
I tweaked the secondary last night before capturing some of this data... I think it helped with the elongation, but I might have overdone it, looked like the bottom right corner got a bit more elongated whereas earlier it was the top left that was the worst. I still had some subs which were showing up as high 0.4's for eccentricity (you don't want it any higher than 0.4 for those unfamiliar with the measurement)
When it nails focus it seems to do ok... see the attached aberration inspector output of a 60s sub from last night. Still looks elongated (and switching either side of focus) when out of focus though. Maybe SGP was just doing a better job of focus on M83 so it didn't manifest there...
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