Making the Most of Aperture Mode

Your digital camera's automatic or program mode is a wondrous thing. It's really amazing how it can take good pictures in a diverse array of lighting conditions.

There are times, though, when you and your camera have a difference of opinion regarding what constitutes a good picture. At times like those, it's a good idea to experiment with some of your camera's other exposure modes. In particular, most digital cameras have a pair of modes that can help you get a little more creative: aperture priority and shutter priority. In this Here's How, we'll talk about the aperture priority mode.

Why Use Aperture Priority?

Okay, let's get this out of the way along with similar questions, like "Why do I need to eat my vegetables?" (because they're good for you), "Why do I have to clean my room?" (because I said so), and "Why mess with the camera's ISO?" (so you can take pictures in dark conditions without a flash).

Aperture priority lets you select the size of the camera's aperture, the opening that controls how much light reaches the sensor at the moment of exposure. A large opening (counter-intuitively represented by a small f/number), makes a picture with a narrow depth of field; a small opening (a large f/number) increases the depth of field, so more of the picture is in sharp focus.

We've already covered this in . Also, check out for more tips.

Dial A for Aperture

Switch to your camera's aperture priority mode by selecting the "A" or "Av" symbol--typically on a dial on top of the camera, though you might need to enter your camera's on-screen menu system. Once selected, this mode lets you choose the aperture at which to take pictures. The camera automatically selects the proper shutter speed in response--so it's a pretty safe way to take pictures, because the camera is still doing half the work.

Try It Out

The best way to get used to using aperture priority is to experiment with it on a lazy afternoon when you don't need to worry about taking great pictures. If you can convince some friends or family members to pose for you, position them a few feet in front of each other and take a series of photos, each one at a different f/number.

You might get something like this pair of photos: In the first image, both subjects are clearly in focus; in the second, only one is in focus.

Note that where you focus has a bearing on your final image. For example, focus on the foreground subject when using a small f/number, and the background subject will probably be out of focus.

Here's another tip: the farther away that you focus, the deeper the depth of field will be. So focusing on the subject in back will yield more depth of field than if you focus on the closest subject, even at the same aperture setting.

Distance Matters

Knowing the relationship between aperture size and distance is handy for photography trivia games, and it can sometimes help you take a better photo of people sitting on a hill, but it's critical for success when you take close-ups, or macro photography. (DOFMaster has a useful online calculator.)

The closer your subject is to the camera, the more narrow your depth of field becomes. If you're shooting something that's only a few inches away--and virtually all digital cameras let you get so close to a dog that you can count the individual hairs on its nose--then the depth of field can be less than an inch. This is the perfect time to switch to aperture priority and dial in the deepest depth of field you can muster.

In this image, for example, the globe is less than an inch behind the astronaut--yet at f/2, the two can't both be in focus at the same time. But by shooting with aperture priority, I was able to set the depth of field deep enough to get an effective shot anyway.

Shutter Priority: What Good Is It?

When you get right down to it, the camera's aperture and shutter do essentially the same thing: They regulate the amount of light reaching the sensor to record a picture. If you have a wide-open aperture, the shutter will open for a relatively short time. But close the aperture to admit less light, and to properly expose the photo you'll have to lengthen the time that the shutter is open.

However, the aperture and shutter controls affect a photo very differently in other ways. On one hand, your choice of aperture determines a photo's depth of field. The shutter, on the other hand, makes a photo sharp or blurry, depending upon how long it's open.

Selecting Shutter Priority

Most digital cameras (except for inexpensive auto-only models) have a shutter priority shooting mode. To get to it, select the "S." On some cameras, especially Canon models, shutter priority is represented by the letters "Tv." Either way, once you select this setting, you can freely choose the shutter speed and the camera will set the matching aperture to properly expose the photo.

Getting Good Results With Shutter Priority

What's the right shutter speed to choose for a given situation? Your main concern, at least in the beginning, should be using a shutter speed that's high enough to eliminate any shakiness caused by holding the camera. In normal daylight--assuming that you have fairly steady hands--consider 1/30 second the slowest acceptable speed unless you brace the camera somehow. If you have a handy wall, door frame, or tree to rest against, you might get good results at 1/15 second.

And those numbers are when you're zoomed out, with the lens set at a wide angle or "normal" focal length. If your camera has a beefy lens 3X zoom (or more), you might need to shoot a lot faster to freeze the action. In the world of 35mm film cameras, we used a rule of thumb that said you should shoot at a shutter speed that's the inverse of the focal length. So if you have a 200mm lens, get as close to 1/200 second as you can (that's usually about 1/250 second). With a 50mm lens, you'd get as close to 1/50 second as you could, and so forth. That rule still holds true--so if you have a digital camera with a zoom lens that reaches 200mm or more (in 35mm equivalent), then crank up the shutter speed accordingly.

Follow these basics and you'll get sharp photos with the camera set to shutter priority. Once you master that skill, you're ready to try your hand at action photography, where the shutter priority mode really excels.

Taking Great Action Shots

There are two kinds of action shots. The most common, frequently seen in sports photography, uses the highest shutter speed available to freeze the action. Alternately, you can go for a slower shutter speed and let the resulting blur tell the story for you: Nothing says "this thing was really zipping by!" like a blurry background.

Freeze the action: Even in bright daylight, you might want to increase the camera's ISO setting in order to get a very high shutter speed, which will help you to freeze a fast-moving subject.

What's a fast shutter speed? If you're at a car race, an air show, or a sporting event with lots of fast action, then I recommend 1/1000 second or faster. (Many digital cameras can reach 1/8000 second.) In fact, no shutter speed is too fast if it allows you to get a shot that you wouldn't be able to get otherwise. For example, this shot of kids playing soccerwas taken with a shutter speed of 1/1600 second.

Get some blur: To blur the background, try setting a shutter speed of 1/15 or 1/30 second, then follow the action by pivoting your body to track the subject. Press the shutter release and keep moving. With practice, the subject will freeze and the background will be a smooth, dramatic blur, like this.

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