Thanks for the quick reply. I did not consider the impact of the CP on the telephoto. Will have to some more research.Breakthrough X4 Polarizer is also brass.
However, I'm leery of using a polarizer on a telephoto as it seems to require me to tune the AF to something other than normal. I did some tests in this thread, and some others chimed in saying their polarizer also affected a Canon and a Nikon. It wan't far off with the 300mm f/4, but putting the 1.4x TC onto it shifted the AF Tuning 9-10 points verses without the polarizer.
Tests: E-M1X is forgetting the AF Tuning settings.
On a wide angle lens, it requires a lot of sky burning in if I'm not careful of going too far.
The type of AF detection has no effect on the type of polarizer required for a mirrorless camera. It's the effect of the mirror in a SLR camera that can effect metering and AF.IIRC, except on the E-m1x and E-m1 mark II, a linear polarizer may not affect Olympus & Panasonic cameras, because they don't have the phase detect sensors. But the majority of polarizers are circular polarizers to work with phase detect cameras.
I was looking at that B+W filter earlier on and saw where one guy felt his Hoya was sharper in the images on the website than the B+W. Here: http://www.photocornucopia.com/1018.htmlI am using B+W CPL Filter 62mm MRC Nano XS-Pro for this lens since years and I am happy with the result so far.