Digital Photography: Use Your Shutter Speed To Control Moving Subjects.

In photography, the use of shutter speeds to control moving subjects may seem self-explanatory. But beginners be warned: there is more to this important skill than meets the eye.

The main principles of shutter speed and movement are easy to visualise. Your shutter is open for a certain period of time, and any movement that occurs during that time will be captured in the exposure. The longer you leave the shutter open and/or the faster the subject is moving, the more blurring will captured.

Let's say you are photographing a seagull flying past at the beach. At 1000/sec it will be pretty well frozen. At 250/sec it will be fairly sharp, but the wing tips may be quite blurred. At 30/sec the whole bird will be quite fuzzy. Once you get as slow as half a second, the seagull may be just a vague streak of white across the sky.

Most of the time you want to freeze your picture so that everything is nice and sharp, but this is not always the best approach. For some subjects you may want to deliberately blur the moving subject to create a sense of motion in your photograph.

A popular example is waterfalls. You have certainly seen waterfall photos in which the water appears a soft, silky flow of white, rather than as sharp drops of water. This is simply a photo taken at a very slow shutter speed, perhaps half a second or slower. This is an easy effect to capture, as long as you remember a few other important tips as well.

Any photo shot at very slow speeds must be taken with a tripod. Once your shutter speed falls below about 60/sec, your hand movements (involuntary) will cause the picture to blur and become fuzzy. The movement effect in the water is really only effective if the rest of the picture is sharp.

You also need to be sure that nothing else is moving in the photo that you don't want blurred. For example, if you shoot your waterfall on a windy day and the trees are blowing, that movement will also appear as a blur in your photograph.

Note: Just a quick tip for photographing waterfalls; not all subjects look best at very slow speeds. I have found that cascading waterfalls that tumble over rocks look great at shutter speeds of about one second. On the other hand, waterfalls that spill over a ledge and fall straight down often look better at faster speeds, perhaps 15/sec or 30/sec. The bottom line is; experiment. Try a few different speeds for each subject and see which one works best.

The last point to make on the subject of movement and shutter speeds it this: your shutter speed can never be seen in isolation from the other manual settings on the camera.

I am frequently asked the following question. "I tried the slow-shutter speed technique with a tripod, but it didn't work. My photo was all white. What am I doing wrong?"

The mistake here is to forget that when you slow your shutter speed right down, you increase the amount of light in your exposure. If your photo is correctly exposed at, say, 250/sec, it is going to be massively overexposed if you just slow the shutter speed down to one second. If your camera is set to manual, you need to remember to compensate for the increase in light by closing your aperture to a smaller size. In this way you can reduce the light (with the aperture) by the same amount as you increased it (with the shutter speed), allowing you to capture the movement without overexposing the image.

So if your photo is correctly exposed at 30/sec F-4, you can slow your shutter to 1 second, but you also want to close your aperture to F-22 to control the light.

Sound complicated? It can be at first, but with practice you will get the hang of it. This is a skill worth learning, and the reward will be some great photography. Good luck and happy snapping.