jimvanells wrote:
Like any art it depends on what the artist (photographer) wants. The longer the exposure the more "tails" you see in the water and the smoother it gets. Most folks use 1/2 to one second depending the flow of the water. Some water falls a full flow will only take 1/4 to 1/2 second without becoming a total blur. Experiment for your self, try several ND filters and shoot at the lowest ISO you camera will allow.