They also have "Variable" ND filters. These are pretty expensive, and I've always been cautious of them. I think they are basically two polarizing filters, that you can cross at different angles. Mess up certain auto-focus? Mess up your nice reflections? ND filters are cheap, and there really is no need to buy several different values. Pick something like a 2Stop, or 3Stop... [On your digi, how far can you turn the "ISO" down? 25?]