We think of pictures as capturing an instant. In truth, pictures capture everything that happens within the short length of time that the shutter stays open. If the camera or the subject moves at all while the shutter is open, the camera will record that movement with motion blur or camera shake. The shutter rests between the lens and the sensor, and blocks light until you take a picture. When you press the shutter button, the shutter opens for the exact amount of time needed to get enough light to properly expose your picture, and then closes again.
Typical shutter speeds range from 1/60th of a second (for a picture taken outdoors in the shade) to 1/1250th of a second (for a picture taken in full sunlight). However, many cameras can take pictures at 1/8000th of a second, and night photography often requires exposures taking more than 30 seconds. When taking pictures, you often don’t need to think about shutter speed. However, the picture will be blurry if either the camera or the subject moves while the shutter is open.
The longer the shutter speed, the more motion blur the picture captures. Therefore, if you take a picture and the subject is blurry because it’s moving, increase your shutter speed by selecting Sports mode on your camera, using a smaller f/stop number, increasing your ISO speed, or adding flash.
Avoiding Camera Shake
If you’ve ever had a picture come out shaky, you’ve discovered the limitations of your hand-holding ability. Even if you feel like you’re holding a camera steady, your hand is moving very slightly. With a quick shutter speed, you won’t be able to see the movements in the picture. With a slow shutter speed, the movements will be visible. Many cameras warn you if your shutter speed is too slow by displaying a shaking hand icon or by simply turning on the built-in flash. If this happens, you can avoid camera shake by doing one of these things (in order of preference, but not necessarily convenience):
- Attach your camera to a tripod.
- Use image stabilization.
- Use continuous shooting and take multiple shots.
- Use flash.
- Increase your ISO speed.
- Zoom out to a wider angle.
Your posture and the way you hold the camera can also reduce shakiness. Always hold your camera gently and with both hands. If camera shake is a problem, keep your elbows against your torso. If possible, sit down or lean against a wall. Set your camera to continuous shooting mode, exhale smoothly, and hold the shutter down for multiple shots.
Before I get into the mathematics, here’s what you need to understand about photos taken while hand-holding the camera: the more you zoom in, the faster the shutter speed you need. With a wide-angle picture, you can hand-hold photos at very slow shutter speeds. With a telephoto picture, you need a shutter speed four to eight times faster. Therefore, if a telephoto picture comes out blurry, a wide-angle picture of the same subject might be fine. To determine the slowest shutter speed you can use to hand-hold a camera, follow the Reciprocal Rule: Keep your shutter speed faster than your 35mm equivalent focal length. If you’re using a 100mm lens, use a shutter speed faster than 1/100th. If you’re using a 400mm lens, use a shutter speed faster than 1/400th. The more you zoom in, the faster your shutter speed needs to be.
The Reciprocal Rule is just a guideline. Many people (especially kids) can follow the Reciprocal Rule and still produce a shaky picture. They should use a shutter speed twice the 35mm equivalent focal length. If you have steady hands, and you exhale evenly while taking the shot, you might be able to use a shutter speed half the 35mm equivalent focal length.
Camera shake is such a common problem that camera and lens designers often incorporate image stabilization. Image stabilization moves camera elements to compensate for your shaking hands. Image stabilization can allow you to break the reciprocal rule by two, three, or even four stops. That’s a huge difference—a four stop difference allows you to hand-hold in 1/16th the light you normally would. Being able to use a slower shutter speed allows you to use a smaller aperture to get more depth-of-field. It also allows you to use a lower ISO, reducing the noise in the picture. Of course, it’s only useful with still subjects—moving subjects will create motion blur.
Controlling Shutter Speed on Point-and-Shoot Cameras
To use the fastest shutter speed possible on a point-and-shoot camera, select sports mode. If the shutter speed is still too slow, select a higher ISO speed or turn the flash on. If you want to use a slow shutter speed to blur motion, select landscape mode. To further slow the shutter, select a lower ISO speed and turn the flash off.
Controlling Shutter Speed on DSLRs
To control the shutter speed on a DSLR, select shutter priority (S or TV) mode. Then, move the main dial (the small dial next to the shutter button) to select the desired shutter speed. Note that as you choose faster shutter speeds to freeze motion, your aperture increases. As you choose slower shutter speeds to create more motion blur, f/stop numbers increase and bring the background more in focus.