So I asked for an ND8 (3 stop) filter, but the store didn't have one. Instead I bought an ND4 (2 stop) which I figured I would need at some point anyway. But what I really wanted was some silky water effects along the beaches. The problem of course that the bright Australian sunshine (sorry Irish viewers) means that you're rarely short of light for such shots.

This was from my first set of experiments with the ND4. (Which I can't find at the moment, incidentally.) But as you can see, 0.4 at f/22 just ain't cutting it. I'm getting some blur but definitely not the effect that I was after.