Just to point out that the patterns I had around Alnitak (see below) are close to the last image on this thread:
https://www.cloudynights.com/topic/6...filters/page-2
Both are shot using both the ASI1600MM and an Astrodon OIII 3nm filter. My image is more stretched I think. An Astrodon filter (sadly) seems not to be a solution.
In processing, once a liner fit was applied to the O3, using Ha as a reference, some of the issue was quietened down somewhat.