I see these great B & W photos on facebook or flickr and wonder how they are shot. I read where the photographers use ND filters to get the "long shot's", i.e. 30 seconds or up to 3 minutes to smooth the water and the clouds. That gives the photos that silver smooth look where there's not a ripple in the water or any clouds as it all blends to one or close to it leaving an object isolated in the water like a boat or a pier. Does anyone know which are the best ND filters to use. I've read where they now up to ND6, which they've probably been there for years, and now ND8 and ND10. I'm sure they are great for waterfalls too. What does anyone suggest who photographs this way? Thank you.