Thanks guys! That's right Bill the hard edge / halo is definitely a result of this technique and probably something I can address with more work in the star masking / reduction stage to ensure they are of similar size. The image has some other issues as there are only 10 frames of Ha and a couple of wobbly ones that egged the stars but I'm thrilled with the potential of this process so we've got some other targets lined up for collaboration and I have 2 CCDs (mono + colour) to try also if the weather gives me a break
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