I've been hunting down non-spider diffraction for a while too.
First I printed some low profile circular mirror clips. No luck. Next I altered the design to combine an edge mask ring with the clips.
After testing on a star, I saw no decrease in the non-spider diffraction. Curiously the exact pattern of diffuse diffraction spikes and voids was unaffected. I would have thought providing a new edge would have at least resulted in a new pattern, like a finger print, or a CSI bullet rifling comparison.
This lead me to make a secondary mask in case the majority of the diffuse diffraction spikes were coming from the secondary edge.
This did have a small effect on the diffuse diffraction spikes, a couple disappeared, but 80% of the bulk was still there.
Temporary link to star comparison
This made me wonder if the the non-spider diffraction was coming from a rough mirror surface, or leftover machine grinding marks from mass production. I took a way-defocused stacked and averaged star image, to see if I could see any striations.
I think I can see some slight radial marks, but a knife edge test would be better. My coatings are also nearing end of life so maybe its just pin holes and oxidation roughness.
Edited by cmooney91, 19 December 2022 - 11:02 AM.