That depends a lot on how dirty it is.
If you just got Dust on it, it is very easy to clean.
Grease from Fingerprints or any kind of Sticky Stuff is a little more Difficult, but still very much possible.
Scratches and Physical Damage to the Filter Glass itself cant be cleaned, in that case the Filter needs to be Replaced.
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My IR Filter on my 2.1 is currently fairly Dirty and needs to be Cleaned urgently, is possibly even so dirty, that i have to replace it (some of the Stuff on there i couldnt get off on an quick earlier Try, so i might have to just Replace it eventually, seen quite a bit of abuse).
If it helps, i can Film The Process of doing that and post here.
