Curiously, one of the most often-asked questions I receive (aside from inquiries on which camera I use, which is just plain ridiculous) is how I make the moving water in my images smooth, silky, foggy, like cotton candy, etc. It’s curious to me because of how easy it is to do. A camera, lens, tripod, polarizing filter, and some overcast light are all that’s needed to achieve a long shutter speed in order gain this effect.
I call this the illusion of motion since a still photo cannot literally illustrate movement but a long shutter speed can still express it effectively.
But merely saying you need a long shutter speed is not enough information for a beginning photographer. For example, how long is long enough?
For most stream and waterfall images, I usually aim for a shutter speed in the range of 0.5 to 2.0 seconds. The example above has an exposure time of 1 second, which seems just about right for this image. I prefer the illusion of motion in my water images most of the time but I still want to retain texture and detail in the water. Under most circumstances, exposure times over 2.0 seconds renders the water as an unattractive, featureless white smear.
Yet this is not always the case. There are other factors that must be considered before deciding on a desired shutter speed.
1) The volume of water. As a general rule, the greater the water flow, the faster the shutter speed. A heavy waterfall with a great volume of water will lose more texture and detail with a longer shutter speed than a similar waterfall with less water.
2) The focal length of the lens. If you think about it, the water (or any moving object for that matter) must travel a much greater distance to span the image frame with a wide-angle lens than a telephoto.
3) The subject’s distance. Again, the same principle in #2 also applies here. The farther away the stream or waterfall, the longer the water must travel to span the image frame than a closer subject.
4) Personal taste.
Of the four factors listed above, personal taste – or scene interpretation – is probably most important. For example, a relatively slow shutter speed can express grace or fragility. A faster one can project raw power or even violence. In the example above, the relatively fast shutter speed of 1/8 second expresses the explosiveness of the wave as it crashes on the rocks. Had I chosen any slower shutter speed and the detail in the exploding wave would have been lost.
In the example above, I preferred no detail in the water. I wanted this image to reflect pure simplicity and any waves on the ocean’s surface would only be unwanted, unnecessary distractions. A 30-second exposure smoothed out the water, giving me the simple, elegant image I was hoping for.
To achieve shutter speeds of many seconds, you will need a low ISO and/or small aperture and/or low ambient light and/or filtration. As to the latter, I use neutral density filters for long exposures when the ambient light is too bright. Neutral density filters are made of darkened glass which absorbs light without imparting any color cast to the image.
For beginners, a 3-stop ND Filter is a good start. A 10-stop ND Filter will allow for much longer exposures even in bright sunlight, but it’s difficult to focus and compose the scene in the viewfinder since the filter is nearly opaque.
A third alternative is the Singh Ray Vari ND, which allows you to change the strength of the filter to fit each lighting situation.
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