Hei Duo-Narroband Shooters!I am currently using an OSC camera and I really enjoy duo-narrowband filters. I started with an Optolong L-eXtreme, which was one of the first filters of this category on the market. Unfortunately, it caused some very unpleasant halos. Many other products followed, and for most filters the performance gradually improved.Since I was fed up with the halos, I set out to find one of the best duo-narrowband filters on the market. In this process, I acquired various filters, borrowed some, and contacted manufacturers. Unfortunately, Optolong and Antlia were not very cooperative. However, I had some contact with Player One and Altair.Altair even provided me with some of their new "Ultra" filters at the time. It turned out, however, that some of their earlier filters had some problems fullfilling the specification, leading to further iterations of the filter-design. One of the first final samples (Altair Ultra 4nm Ha-OIII) is also included in the test and showed great results.In the end, the following filters were tested and measured:    Optolong L-Extreme
    Antlia ALP-T
    Player One Anti-Halo Pro
    Altair Ultra 6nm Ha-OIII (preliminary version)
    Altair Ultra 6nm SII-OIII (preliminary version)
    Altair Ultra 4nm Ha-OIII (preliminary version)
    Altair Ultra 4nm Ha-OIII (final version)A considerable amount of time and effort went into the measurements, tests, and evaluation. Therefore, it would have been a shame not to share this information with others. I hope this document helps you out if you are also searching for a duo-narrowband filter.You can access the full document via my Google-Drive. So if you are interested, you can download it from there.If you have any questions, comments, feedback, corrections, etc., feel free to reach out to me.Best regards,
Florian