I used 2 different ND filters. A B&W ND 1.8 (106) will decrease exposure by 6 f-stops. This filter works well in shady locations. If I shoot in bright sunlight I like to use the B&W ND 3.0 (110). This filter will decrease exposure by 10 f-stops. I like to shoot at F8 or F11 to achieve the sharpest images. The tripod and remote shutter release are necessary for the long exposures. Shutter speeds I like to use are anywhere’s from 4 seconds to 30 seconds depending on the speed of the water. If you try this for yourself. Experiment with different speeds and see what you get.