♦ Reflection blocker coating against reflections in combination with correctors placed near the filter
♦ Exact and narrow half-widths for optimal signal-to-noise performance
♦ Identical filter thicknesses for homofocality
♦ Blackened edges
♦ The front side is marked in the form of a black outer rim
To me, these seem to be optimizations targeting mitigation or elimination of microlens diffraction artifacts. Antireflection features, clearly marked front side, blackened edges...these are things that people on these forums have been talking about in particular in recent months, especially with regards to the IMX455 and its occasional microlens diffraction issues. I am not sure if both sides of the filters are AR coated...I've heard that for interference filters (i.e. NB) that's not possible...but this does say the reflection blocker coating is for use in combination with correctors. A bright star could easily enough cause reflections off of multiple surfaces as microlens-diffracted light bounces off the sensor back up the optical path...the sensor coverslip (both sides), the sensor window in the camera (both sides), the filter (both sides), and any corrective optics.
I think that it is more important to have the anti-reflective side of the filter facing the sensor. Otherwise, the more reflective side can and will (and DOES) reflect those microlens grid patterns back to the sensor. The fact that this here states the reflection blocker should face any corrective optics makes me wonder about how optimal they really are for CMOS sensors, but I guess someone will just have to test them out and see.
Anti-reflective properties are clearly a critically important part of the design of CMOS cameras. The sensor cover slips, the sensor windows in the camera bodies, and the sensor-facing side of filters, should all be coated in high quality multi-layer anti-reflective coatings to minimize or eliminate microlens diffraction, IMO.
Edited by Jon Rista, 12 May 2021 - 10:10 PM.