B and W kasserman 77 mm circ polarizer

Hi there,
I just got this filter and took it for a run with my new 17-40, but got some smudge on it ((
Sorry to ask such a basic questions. I am really scared of cleaning it.
What equipment do i need to get rid of this smudge ?
Will a microfiber cloth do? What do i need to buy to clean it without scratching it?
Thanks much for your insight.

Microfibers are fine. If that doesn't do the job a damp lens tissue (not silicone-treated) can often do the job. I often use a dab of saliva on the lens and lens tissue to do the job if nothing else works.

They're not particularly fragile. Anything you'd use to clean a lens would be fine.

Be aware the polazing filters have protective coatings, the good ones do at any rate. I have noticed this while cleaning my Hoya HD and Pro1D circular polarizers. This could make cleaning it more complicated than a lens. Don't freak out if you can't get it cleaned as easily as you would think. Smart asking here first. Be careful and take your time.

B+W multicoated filters clean as easily as any lens I've owned using Kodak (now Tiffen) lens cleaning paper and Kodak (again, now Tiffen) cleaning solution.

DANATTHEROCK wrote in post #10228886
Be aware the polazing filters have protective coatings, the good ones do at any rate. I have noticed this while cleaning my Hoya HD and Pro1D circular polarizers. This could make cleaning it more complicated than a lens. Don't freak out if you can't get it cleaned as easily as you would think. Smart asking here first. Be careful and take your time.

Your lenses have essentially the same kind of coating, but Hoya filters have a long-established reputation for being hard to clean.