Being the paranoid type, I have always paired my lens purchases with (what I see as a requisite) skylight/uv filter purchase. Obviously, this serves to keep my lenses - the front elements, anyways - in something approaching pristine condition. That said, all the grime etc., deposits itself on the said skylight/uv. The problem: How to clean these things? My efforts never seem to meet my satisfaction. Streaks, spots, etc. always remain. I use Kodak/Tiffen lens cleaning fluid and paper. I have also tried various cleaning pens. Both to no avail. So... how do you clean your filters?