"...For example, Tiffen and B+W have 0.3, 0.6 and 0.9 ND filters for reducing one, two and three stops of light. Hoya, on the other hand, uses 2×, 4× and 8× to indicate reducing 1 (i.e. 2=21), 2 (i.e., 4=22), and 3 (i.e., 8=23) stops. The two ND filters come with Nikon's Coolpack are of ND4 and...