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I have seen similar with a Baader 7nm Ha filter. In that case I believe it ended up being poor coatings on my particular Baader Ha which generally have a good reputation. Some said it was likely a mismatch of darks and lights but even reshooting darks made no difference.
So its either:
1. defective coatings with holes in them
2. mismatched darks and lights. Can you post your dark?
Also if you use median combine you are less likely to see these sorts of artifacts that thrive if you use sum combine where all defects get added together with no outliers being removed.
Greg.
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