Dostałem dzisiaj odpowiedź od Marumi w sprawie filtra CPL Sunpak/Marumi. Oto ona:
We have developed and designed the world first innovated coating of DHG for
specially for DSLR and we are not sure about Sunpak product with out
checking their product. The Sunpak has their own factory in China so it
would be not easy to reply about it.

For reference's sake, we produce 300,000 pcs of filter per month and supply
to major camera manufacture, lens manufacture, filter manufacture and
importer with 20 over brand. We have our policy that we are not allowed to
inform those brand.

Myślę, że wszystko jasne.