I have been interested in capturing long exposure effects for a while now. On the Summer School and Progression Courses we have really enjoyed going out to waterfalls for this purpose. Just being outside and hearing the sound of flowing water does you a lot of good. I thought I would pass on some techniques for capturing these startling effects.
You need a tripod and neutral density filters. For under £10 you can get a perfectly usable pack of filters to get going. Personally I use a Hoya ProND1000 which has a 10 stop light blocking capacity and is made with optical grade glass. The filter(s) need to fit the thread on the front of your lens, of course. If you are making a long term investment the Lee system of filters is a very good choice.
At the location compose your picture with the camera on the tripod then attach the filter to the front of the lens. Neutral density filters are very dark and are not easy to see through. In manual exposure mode set 100 ISO, f/11 and 15 seconds. As to focusing, try auto focus (AF-S single servo) with 1 area (small box) pointed at a rock or other fixed point. You will need something fixed and unmoving in your image to provide a contrast with the movement of the water. It may be too dark with the filter for the auto focus system to function and the camera will not take a picture. If this is the case, focus in manual mode (MF) with the filter removed. Then carefully attach the filter without jiggling the lens. This is a bit fiddly but it does work.
Take the picture. You will hear the shutter open and then close some time later. The camera will take a while to process the information from this long exposure. If the image is badly exposed use the aperture to increase or decrease the amount of light entering the lens. Then alter the shutter speed if you need to. The effects you obtain will also depend on the amount of movement in the water. It can vary from an overall ‘glassy’ look to an appearance of steam or fog.
It really is great fun waiting to see what will emerge from the process. Give it a go!