This reminded me that I did do a sample OIII image the other night. It is the same camera settings (Unity, 5 min. sub) and same focus as the Ha. One thing that throws off the comparison is my Ha filter is the 5nm bandpass and the OIII is 3nm. Anyways, the pattern is clearly visible in the Ha, and not visible in the OIII, but I figure that just comes down to the 3nm OIII not letting in as much light as the 5nm Ha. So, not conclusive, but still interesting.
Astrodon H-alpha 5nm
The pattern is definitely present in this image. It is faint, but you can see arcs reflecting off neighboring microlenses for this big star. There are four primary ones, all at 90 degree angles rotated by 45 degrees (so, starting at 45, then 135, then 225, then 315). I would attribute the difference between the intensity of the pattern in your image to the difference in aperture (in terms of area, your scope has 3.5x LESS aperture area than mine, on top of the difference in f/ratio).
The star really does have to be BRIGHT. In my case, they are always heavily clipped, because they saturate in mere seconds even with NB. It may be that some people who have not had the problem yet are just not imaging bright enough stars. It may also be that the pattern is there but very faint.
Here is an example of the issue with my setup:
@Mark, I forgot that I actually acquired frame sequences in multiple filters a while back. I'll process and share those when I get home, on the original thread I started on this issue. Hopefully you can confirm (or refute) whether it is indeed microlens diffraction or not. Based in my experience imaging Pleiades, the pattern is indeed different in each color channel...however with broadband filters it is tougher to identify the microlens reflections. Hopefully I have both Ha and OIII data at home that I'll be able to share.
Edited by Jon Rista, 01 February 2017 - 01:53 PM.