I conducted a halo test of the new Antlia Pro 3nm narrowband filters, using Sirius as the target.
All exposures were 2 minutes with the FSQ-106EDXIII running at f/5, 2" (48 mm) filters on the QHYCFW3-L, QHY600m camera set at 27 gain and 18 offset cooled to -5 deg C.
Here the captures with intensity adjusted based on equal brightness of background stars. Halo assessments with my configuration are:
The diameter of the halos were the same around other bright stars in the field. This indicates the reflections are likely between the two faces of the Oiii filter. I notice, in the case of the Oiii filter, the shiny, first surface filter coating faces toward the camera sensor, away from the telescope objective, while the Sii and Ha filters and LRGB filters all face the other direction. Antlia states that face direction should not matter and that halos are to be expected with the Oiii filter.
I hope these test results are informative.