One of the most interesting (and challenging) subjects to shoot is moving water. With most cameras, you could set a quick shutter speed and “freeze” the scene. But a far more dynamic picture can be obtained if you mount your camera onto a tripod and use a long shutter speed to capture the movement. Fast moving water will turn up silky smooth when the shutter speed gets sufficiently long.
If you’ve experimented with this technique before, then you’ll know that there’s only so long you can leave the shutter open. Beyond a certain shutter speed, the picture deteriorates very quickly, becoming over-exposed in the brighter areas. With this particular image, the shutter was left open for a full minute, something normally impossible under daylight conditions. This is where neutral density (ND) filters come in. Think of these as “sunglasses” for your lens. They reduce the intensity of light that passes through your lens, without altering the color of the scene. These filters come in various strengths, ND2, ND4, ND8, ND16 etc., with higher numbers indicating a higher density. [Hoya’s ND400] was used for this image.
There are a few things to note with such filters.
a) They will likely prevent you from viewing the scene through the viewfinder/ LCD once they are mounted. You should frame the scene and switch to manual focusing before you mount the filter.
b) Any exposure reading taken by the camera will be inaccurate, so switch to bulb mode ([what’s that you ask?]) and use a remote shutter release to eliminate camera shake. Bulb mode can be intimidating, as it is pretty complicated to calculate how long you should leave the shutter open. The best way is to experiment with the scene and increment your shutter speed by 5 to 10 seconds per shot.
While it sounds endlessly complicated, it really isn’t too bad, and you’ll get fantastic images at the end of it.