I’m a big fan of lens filters — primarily for lens protection as I would rather break and scratch a filter than an expensive lens.

My preference are B+W filters with MRC coatings.

When they get dirty (which they will) B+W recommends the following:

If dust, water or dirt has to be removed in spite of all the precautions, please take the following rules to heart:

Never rub dry dirt or dust off the surface, because they may contain miniscule quartz particles that are much harder than glass and that can scratch the latter nearly as badly as diamonds can.

First gently whisk the dust off with a very soft brush before breathing on the surface and then using a soft cloth, preferably the B+W “Photoclear” microfiber cleaning cloth and extremely gentle pressure to wipe the surface clean.

When the dirt is very hard to remove, a bit of saliva is the best solution – always available, guaranteed free of abrasive materials, oil and aggressive chemical substances. Never use a paper tissue for cleaning because it leaves too much lint, and paper fibers cling to glass because of electrostatic charges.