With stunningly fast shutter speeds, today's cameras can stop almost any motion. But some subjects-such as race cars and babbling brooks-become more interesting when you emphasize their motion, letting the action happen during the exposure.
Usually, you indicate motion by blurring either the background or the subject of the photo. To do this, you have to take control of your camera's shutter speed, aperture, and ISO settings. Once you understand how these three settings work together, you can use them to convey almost any type of motion. And the best news is, you don't need a fancy camera to get the job done-any camera with a shutter-priority mode will work.
Managing your light
Motion blur is controlled by your camera's shutter speed, which is the amount of time the shutter stays open so light can hit the camera's sensor. If something in the scene moves while your shutter is open, it will blur in the final image. This means that slower shutter speeds generally show more motion blur.
To change shutter speed, put your camera in shutter priority mode (often indicated by the letter S or a TV icon) or in manual mode. Shutter speed is expressed as a fraction of a second. Though how this appears can vary from camera to camera, typically, a shutter speed of 1/60 represents one-sixtieth of a second, while a number without a fraction refers to whole seconds (so 2" is a two-second exposure). While the exact definition of a slow shutter speed depends on the situation, anything slower than 1/15 usually qualifies.
As more light hits the sensor, you run the risk of overexposing the image, which will wash out all the colors and blow out the highlights. One way to counteract this is to adjust your camera's ISO to a lower sensitivity (for example, ISO 100).
You can also manage light by changing the aperture. This opening widens or narrows to control how much light hits the sensor. If you're shooting in shutter priority mode, the camera will automatically calculate an appropriate aperture for whatever shutter speed you've chosen (you'll usually get a warning if it can't achieve the setting). If you go fully manual and are getting too much light, you'll want to stop-down, which means choosing a smaller aperture. Because apertures are fractional, f/2.8 is a larger opening than f/22.
Even if you lower the ISO and choose the smallest aperture possible, you may still get too much light. In this case, you can use a neutral density filter. These glass or plastic discs typically screw onto your lens and reduce the light that reaches the sensor. They come in different values, offering anywhere from a 1 f-stop to a 10 f-stop reduction in light, and are sized for different lenses. They're worth the cost (prices range from $10 to $200), but if you're up a creek without a filter, try putting your sunglasses in front of the lens. It just might do the job.
Once you understand the basics of getting a good exposure, you can begin experimenting with capturing motion. How you hold and move your camera while the shutter is open dictates the type of movement your shot will portray. Let's start with one of the easiest scenarios: keeping your camera steady as the subject moves through the frame, a river, for example. When blurred, the moving water takes on a dreamy, fluid haze that can convey anything from a slow trickle to a powerful gush. The lighting and speed of the water will determine your exact shutter speed. A good starting point is your smallest aperture (f/22 on most cameras) and then a shutter speed of about one second.
Keep in mind that when you leave the shutter open, you run the risk of introducing another type of movement: camera shake. The best way to combat this is to attach your camera to a tripod. If a tripod isn't around, put the camera on a solid surface and set its self-timer button to trip the shutter.
This technique is great for nighttime street scenes as well. By putting your camera on a tripod and using a long shutter speed (try one second to start and an aperture of about f/5.6), moving traffic will look like streaks of white and red. Review your results and then increase or decrease the shutter speed as needed. A slower shutter speed will produce longer streaks of light, and a faster shutter speed will result in shorter streaks.
If you're using shutter-priority mode for nighttime images, you may find that the camera's auto exposure settings make the scene a little too bright. To darken the background so it's clear you're shooting at night, go to the exposure compensation feature on your camera and choose -1 or -2.
Panning for gold
Another way to show action is to keep the moving subject sharp while blurring the surrounding scene. This involves panning, following the subject in the viewfinder. It's particularly effective at sporting events.
Say you're shooting race cars. Use a high shutter speed, and the car might look like it's parked on the track. Use a slow shutter speed, and the car will be a blur in your photo-good for some images, not for all. But if you use a shutter speed of around 1/125 of a second and move the camera in the direction the car is traveling, not only do you blur the background, but you also blur the wheels.
Start by prefocusing on the area where the subject is going to be when it's in front of you. If you're in auto-focus mode, point at the spot where the car will drive by. Depress the shutter halfway and, while still holding the shutter down, swing the camera so that the subject stays in your viewfinder. Then press the shutter when the car is in the prefocused area and continue following the subject through and beyond the shutter click.
This technique works best for subjects that are moving in a plane parallel to you. Bicycles and skateboards also make great subjects (start with a shutter speed of around 1/30 of a second). If you're having trouble panning the camera steadily-especially tricky with longer lenses-use a tripod or monopod for extra stability.
Stuck on you
Stick your camera to a moving subject (bicycles, skateboards, etc.), and the background will be blurred while the object the camera is mounted on-bicycle handle bars, for example-will be sharp.
You can attach a compact camera using a homemade clamp or a Joby Gorrillapod. For heavier SLRs, use something specifically made for the job, like a $27.50 Bogen Super Clamp or a $90 Fat Gecko Camera Mount. Use the self-timer button to trip the shutter so you can steer safely.
Slow sync flash
Combining a flash with a long exposure can also convey a sense of motion. The moving subject of the photo blurs, yet the flash freezes the subject at the very end of the exposure. Try this at a party or night club to convey the movement of people dancing.
Most compact cameras have a night-portrait scene mode or party mode that sets the flash to fire at the end of the exposure. Likewise, if you have an SLR, almost all modern shoe-mounted flashes offer a mode (alternately referred to as a rear curtain, second curtain, or slow sync mode) that accomplishes the same thing.
Want to jump into hyperspace? Zoom your lens while using a slower shutter speed (start around 1/15). Objects at the edges of the frame will appear to move toward the center of the frame. You can also try this with a slow sync flash that freezes the motion of the person you're photographing in the center while the background zooms away.
Trial and error
With all of these techniques, finding the right settings will take some experimentation. Don't be discouraged if there's a high failure rate, especially when you first try them. The beauty of digital cameras is that you can take as many pictures as you like without shelling out a fortune for lots of failed prints. But when you get it right, the results will be worth the effort.
[Jennifer Wills is a professional photographer and designer, and a cofounder of W+W Design.]
This story, "How To: Add Motion Blur to Your Photos" was originally published by Macworld.