Does anyone know what level of UV common UV filters are calibrated for? I always read about people in UK and US swearing by their effectiveness but here in Australia it seems to do nothing, then I realised it's probably because our UV is always so extreme compared to the rest of the world.

I don't really want to have to by 5 of them and stack them, that's more than my camera is worth lol... but like surely someone sells an Australia UV calibrated version?