Here's an update. The dealer was nice enough to reverse the 3nm Oiii Antlia Pro filter in the 2" cell. The results are much better with the coated shiny surface facing the sky away from the camera. The halo is still there, but greatly reduced. Therefore, try reversing the filter direction if you are getting severe halos. The test star was Sirius, and the exposure was at 95% of saturation at the star center. One image is calibrated but no stretch. The other image is stretched to show the residual halo.