There’s a misconception that still photographs are just single frames of what could be a movie. Why do we bother to take still photos when we could just use a video camera to capture the whole scene and select away the single best frame?
The reason is time. A video camera is going to shoot no slower than 1/24th of a second per frame — any slower and a video playing at 24 frames per second speed would move faster than reality.
Unlike video in still photograpy we can choose the slice of time shown. If we leave the shutter open for only an instant we can stop bullets and raindrops in mid flight. If we leave the shutter open longer we can take pictures of the stars and the milky way.
Controlling time is the most obvious when photographing moving water. Do you want your photo to stop each drop in flight or do you want it to appear smooth like silk?
Here are a few examples of different shutter speeds and how they affect the photos.
At 1⁄500 second (left) the individual drops are visible flying in the air. At 1⁄125 second (right) the droplets show trails as they fall.
At 1⁄30 second (left) individual droplets are no longer visible and moving water forms a stream. At 1⁄4 second (right) streams of water stop being visible.
My favorite, and the picture shown at the top, at 1 second the water is smooth like silk.
If you want to take longer exposures like these, close your aperture down as small as it goes — mine was set at f/16. To cut down on light moving through the lens buy a neutral density filter that fits your lens or buy a huge one and hold it in front of your lens. You’ll also want a tripod: for these shots I used a simple Manfrotto travel tripod, it’s a bit heavy but remarkably stable and small.