Since the introduction of Stellarsolver, all the star related operations are delegated to this library. Now I'm facing an autofocusing problem and I think that I can try to track back a fix for it into Stellarsolver... but I'm nor sure, so, here I'm asking for advice.
First, the problem. I've a fast newtonian (150/600, so f4) that has a very shallow CFZ. I've put a coma corrector on it (TS-Optics GPU). And this corrector is introducing chromatic aberration. I'm using a OSC (the ASI533MC), so the images that I capture has the bayer matrix pattern over it. Now, when I use the autofocus module with the ZWO EAF it works fine... only for the red pixels.
I suspect that Stellarsolve is using only R channel to compute HFR and then the autofocus algorithm is focusing on the red extreme of the spectrum. The problem here is that the chromatic aberration shift the focus and I end with a G channel slightly unfocused and a B channel completly unfocused.
You can see the problem if you look at the three channels (show in order RGB)
They are extracted from one single shot. The one chosen by the autofocus module seems to be the first one (R). You can see, that forgiving about the remaining miss-collimation, the R channel has an acceptable focus that deteriorate to G and it's almost completely unusable on B.
My proposal is to change the channel used on OSC images for all the quick computation to G. This way if you have chromatic aberration you will have a perfect focus on G (where you have half of the pixels) and then, then same amount of error for R and B, but overal the image will be on better focus.