This issue’s article has little to do with printing, but a great deal to do with exposing an image—and it applies equally to black-and-white or color, and to digital as well as traditional exposures. It has to do with the length of exposure time for a moving subject, in this case a waterfall.
At the east end of Swiftcurrent Lake in Glacier National Park, the water rushes out in a small, but wonderful display of crashing fury. Only about 60 feet across, and probably no more than a 35-foot drop, the waterfall is, nonetheless, quite spectacular. The question is: what is the most appropriate shutter speed to best convey your impression of that waterfall?
Most people are very confused about the “correct” shutter speed to use under these circumstances. Some people like to stop the motion so that every drop of water is caught motionless in mid-air. Others prefer a soft blur of the water’s motion. Some people strive for something in- between. But still the question persists, what shutter speed will give you the effect you want?
This question often comes up in workshops that I teach, and surely comes up whenever we encounter moving water, especially a waterfall. The concept I try to get across is how much of the film plane would be traversed by any single molecule of water during the length of the exposure. Once you can envision that, you’ll get close to the shutter speed you want.