What Does the Shutter Speed Setting on Your Camera Do?

There are three basic settings that affect the exposure of your picture - aperture, shutter speed and ISO rating. Combined, these three settings determine how much light is allowed into your camera.

You need to balance all three settings to let in the right amount of light. Too much light leads to a blindingly bright, over-exposed photo. Too little light leads to a dark, under-exposed photo. To make things more complicated, each of these settings has a unique side effect that can impact the final look of your picture.

So what, specifically, does the shutter speed do? And what is the side effect of increasing or decreasing the shutter speed?

Shutter Speed - How Long the Camera Lets Light In

When you press the button on your camera to take a picture, the camera opens the shutter - a little door covering your film (for a film camera) or the sensor (for a digital camera). If you left this open for a long time, you'd let a lot of light in. If you only left it open for a fraction of a second, you'd only let a little bit of light in.

The amount of time that this shutter is left open is the "shutter speed" that you're using. Shutter speeds are commonly measured in fractions of a second. If you see "1/30" on your camera, that means the shutter will stay open for 1/30th of a second. If you see a number with a quotation mark after it (like 1"), that means that the shutter will stay open for that many seconds. This is, however, uncommon... unless you are leaving the shutter open for a specific purpose.

When there is a lot of light, you'll need to use a high shutter speed to restrict how much light comes in. This varies with the other settings on your camera, but you might need a shutter speed of 1/500th or 1/1000th or a second on a really bright day. On the other hand, low-light situations call for slower shutter speeds to let in enough light.

What About that Side Effect?

Besides letting in light, your shutter speed can also lead to one really nasty side effect - motion blur.

In order to catch a nice, crisp image, your subject (and the camera) needs to remain still while the shutter is open. If the shutter is only open for 1/400th of a second, this is pretty easy. Even a football player running down the field will move very little in that time span.

But what if the shutter is open for a full second? Chances are your subject will move, and chances are also pretty good that your hands will shake. The result? A blurry picture.

If you take pictures of sports, this can be of huge concern. Relatively slow shutter speeds (i.e. 1/30 or 1/60) are going to be no good. Your pictures will definitely be blurry. When I take pictures of sports, the minimum shutter speed I shoot for is 1/125, and this will often lead to sub-par results. 1/250 is usually a satisfactory compromise, but 1/400 or quicker will make for nice, sharp images. Of course, this can also vary with the direction in which your subject is moving and you'll have to experiment a bit.

A second problem, camera shake, can also occur due to low shutter speeds. As you increase the focal length of the camera (i.e. as you zoom in), you need to hold the camera steadier to prevent the picture from being blurry. If you're zoomed in extremely close (i.e. 400mm), you're going to have a hard time stabilizing a camera. If you're at a wide-angle zoom of 20mm, you won't have much trouble at all. A general rule of thumb is that your shutter speed should equal your focal length. If you're using a 50mm zoom, you need at least 1/50 for a shutter speed. A 200mm zoom calls for a 1/200 shutter speed. So on and so forth.

Using a monopod or tripod can help solve this problem. You might also find relief from some kind of vibration reduction or image stabilization feature on your camera/lens. But, the surest way to ensure that you don't have any camera shake is to increase the shutter speed on your camera.

So When Should I Use Shutter Speed Priority Mode?

Your camera probably has four basic modes - programmable auto, aperture priority, shutter speed priority, and manual.

You'll want to use shutter speed priority when you need to maintain a certain shutter speed. The most common reason for this is that you're shooting an action sport and there's not enough ambient light.

For example, let's say you're shooting a football game at night. To get a properly exposed image, you might have to use a shutter speed of 1/60 or 1/125 (despite having the aperture wide open and having the ISO cranked up). This gets the light in, but it doesn't eliminate the motion blur from players running back and forth.

What's worse - motion blur or darkness due to underexposure? Motion blur. An image that is underexposed by one or two stops can be salvaged in post-production with an image editing program like Photoshop, Lightroom, or GIMP. But if you have motion blur, you're out of luck. No amount of editing will get rid of that blur and give you back a nice, crisp image.

In a situation like this, when you need to ensure a minimum shutter speed, you'll want to switch to shutter speed priority. Your camera will create under-exposed images, and it might not be happy about it. But at least your subjects won't be blurry and you'll have something useful at the end of the day.