My Canon G12 camera has an internal neutral density filter that can be applied inside the camera with the click of a button. A neutral density filter is designed to reduce the amount of light hitting the camera’s sensor without affecting color. This allows the photographer to open the shutter for longer periods of time while still accurately recording the amount of light and color in a scene.
This technique can be used to blur (or erase) moving objects, and is best used with moving water or busy city streets. It can give a photograph with moving objects a slightly more dreamy quality than an average snap-shot.
The picture above is a fifteen second exposure of Lake Winnebago at dusk. Please notice the somewhat smooth dreamy reflections in the water. (The motion blur of the water causes this effect).
The snap-shot below was taken earlier in the evening and from a different location, so it may not be the best comparison, but please notice the sharper detail in the water.