I've recently ran into this issue as well. I've had my Octopi attached to my RASA 11 v2 for about a year. I run the rig with an ASI6200MC camera as well.
Not until about 2 weeks ago when I got serious about leveling the tilt of my camera via the Octopi did this 'rainbow glare' issue begin. Before I got all four corners of the tilt adapter within 3-5 microns of each other was this 'effect' an issue. My stars evened out with adjusting the tilt, but this glare effect started. Ugh. haha
I can get the flocking paper easily, but I'm concerned with cutting it accurately. How did you guys cut it with precision?
PS. If anyone would care to sell me a 3D printed ring I'd be interested, but the one posted here is for an APS-C sensor and not a full frame, so I don't know if it'd even work. I do not own a 3D printer.
It will take trial and error to get the size right.
I suggest a good circle cutter
https://www.amazon.c...,aps,111&sr=8-3
and some adhesive light blocking felt
https://www.amazon.c..._images_section