Capturing those dreamy, blurry waterfalls, river rapids, and rolling waves is simple once you figure out the basics of using a tripod and setting a slow shutter speed. You might notice, though, that some parts of your photos turn out overexposed. The problem is that the total range of exposures, from the bright, reflective water to the darker foliage and rocks, is greater than your camera is capable of capturing in a single shot. One popular solution is to use a neutral density filter. A neutral density filter screws onto the front of your lens (if your lens has threads, as do most digital SLR lenses, and some point-and-shoot cameras) and reduces the amount of light reaching your camera's sensor. That will help reduce or eliminate the worst of the overexposures.