Time Bracketing

Whether Using film or digital, photos benefit from employing time to freeze or blur motion

By Bruce Barnbaum Back to

Barnbaum_JF_2008_1

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.

Distance and shutter speed

Suppose you have a slow-moving stream carrying a few fallen leaves with it. If the leaves are far away, they may move very little during a full second of exposure. Yet if they are close to the camera—although moving at the same slow rate—they may completely cross the film plane during that exposure. On the other hand, a fast-moving particle may produce a slight blur at 1/125 second even if it’s quite a distance away, and it will surely cause a huge blur if it’s very close to the camera.

So, we have a combination of two things to consider: the speed of the moving entity and its distance from the camera. A slow-moving object very close to the lens may appear to move farther than a fast-moving object far away because it may traverse a larger section of the film plane during the exposure than the fast, distant object.

In the case of Swiftcurrent Fall, I was standing on a precipitous edge above the river just below the fall, looking at it from a distance of about 200 feet. From my point of view, it was almost in a single plane perpendicular to me, making everything almost equidistant from me, while also reducing depth of field to a very minor problem. This gave me the option of being able to shoot it at a variety of shutter speeds while changing the aperture without losing significant depth of field on the waterfall.

I chose three shutter speeds, using my 210mm lens on a 4X5 Linhof Master Technika camera: 1/60, 1/15, and 1/4 second. I felt that these three speeds would give me the full range of possible effects that could have been pleasing to me.

At 1/60 second the water is nearly stopped in mid-air at the top of the fall, where its velocity is still relatively slow. But you’ll notice that at the bottom of the image—especially in places where the water is in virtual free-fall, such as along the right edge—the water is starting to blur considerably. To me, exposing this at any faster shutter speed would have negated the impression of moving water because virtually everything would have been stopped motionless or nearly motionless. But at this shutter speed, the impression is one of wild and rugged motion.

At 1/15 second, the water is taking on the impression of movement every- where. It has a bit of a rugged feeling, but not as much as that of the faster shutter speed. Notice that the upper part of this image has somewhat the same feeling of movement that the lower part of the 1/60 second exposure has, which tells you that water at the bottom of the waterfall is moving about four times as fast as at the top.

At 1/4 second, the water has a smooth, soft effect throughout, which some people have described as “cotton- candy.” (If you go to still longer exposures the effect becomes even softer, but not by much.) Some people hate this effect; others love it. It certainly is a far more lyrical effect than that of the fastest speed. Notice that the water separates most distinctively from the rocks at this speed, as opposed to the fastest speed, where it may be difficult to tell if you’re looking at rock or water in some places. At this slowest shutter speed you can even judge the shape of some of the rocks under the flowing water, which is virtually impossible with the fastest shutter speed.

Your choice

Which effect is best? It’s up to you to decide. They each have qualities that are unique and quite distinct from one another. If you want to show both the rugged, wild feel and the lyrical feel at the same time, you may be out of luck. Some people may say that the middle length exposure does that perfectly, while others will say that it’s neither here nor there, failing to convey either of the impressions adequately.

The point of all this, however, is to get you to think not just of bracketing for the proper exposure (which almost everyone does during the learning process), but to consider bracketing for time on a moving subject, so that you can better determine which shutter speed gives you the impression that you want to convey.

Another point that it may subtly bring up is: how does the eye actually see it? I suppose that varies from person to person, but my guess is that nobody sees it in real time like the 1⁄4-second exposure, though some may see it very much like the 1/60-second exposure. Does that make the 1/60-second exposure more realistic? Probably. Does it make the 1/60-exposure better? Not necessarily. I don’t think photography has to be realistic to be effective … and in many cases it can be most effective when it departs from reality, giving us a view of the world that we don’t necessarily see. This, in itself, is a topic worth your best consideration.


About the Author

Bruce Barnbaum
BBarnbaum
Bruce Barnbaum teaches photography workshops throughout the year, focusing on the art of seeing and the art of conveying impressions of your photographed world (real or imagined). He has two monographs in print: Tone Poems - Book 1, 2002; and Tone Poems - Book 2, 2005. Both are collaborative efforts, featuring a CD of classical piano music performed by Judith Cohen. www.barnbaum.com