Having some problems here guys. I have a 67mm Marumi CPL, which I have used for quite a long time. I keep it clean with a blower and some microfiber.
However, until yesterday, I didn't notice some dust and small smears apparently on the surface. But when I tried to clean them, they were found to be between the two layers of the glass.
Is there any proper/alternate way to clean the CPL filters? Am I missing something?