Heliopan39mm UV Filter (703901) with specialty Schott glass in floating brass ring

Heliopan and B+W both make fine filters, and I've never found either wanting. I use this on my Fujifilm 27mm f/2.8 pancake lens. As I often carry it without a lens cap, I keep this filter on all of the time. My only wish is that it were a bit thinner. Granted in needs an element of depth to have threads to hold a cap, but it seems a bit thick compared to my thinnest B+W filters (which can hold a cap), and given that I use this on a pancake lens, any bit of depth saved would be appreciated. Otherwise, it's rather nice.