What Is Aperture Priority Mode?

Aperture controls depth of field

Photography camera set on tripod at sunset

Kiyoshi Hijiki / Getty Images

One of the easiest ways to improve your photography is to master depth of field. This concept relates to the relative distance in your photo between the nearest object in focus and the farthest. Images with shallow depth-of-field settings present the foreground crisply with the background faded and blurred.

Aperture priority mode on a digital single-lens reflex camera determines depth of field.

What Is the Aperture?

The aperture setting controls how much your camera lens opens to capture the image you're shooting. It works like the pupil of an eye: the more the pupil dilates, the more light and image info are admitted into the brain for processing.

Photographers measure the size of the aperture in f-stops—for example, f/2, f/4, and so on. Contrary to what you might expect, the larger the number in the f-stop is, the smaller the aperture is. Thus, f/2 denotes a larger lens opening than f/4.

Think of the f-stop number as the amount of closure: A higher number means greater closure.

Using Aperture Priority Mode to Control Depth of Field

Aperture size works with shutter speed to determine the depth of field. Imagine a landscape shot in which only the first few inches of the image are sharp or a photo of a chair in which it and its background are in equal focus.

To select aperture priority mode, look for the A or AV on the mode dial on the top of your DSLR or advanced point-and-shoot camera. In this mode, choose the aperture, and the camera will then set an appropriate shutter speed.

Tips for Shooting in Aperture Priority Mode

depth of field

When you're shooting a landscape (which requires a wide or large depth of field) choose an aperture of around f16/22. When you're shooting a small object such as a piece of jewelry, however, a narrow depth of field will help blur the background and remove distracting details. A small depth of field also can help pull a single figure or object out of a crowd. An aperture of between f1.2 and f4/5.6, depending on how small the object is, would be a good choice.

Don't forget about the shutter speed when you're concentrating on your aperture. Normally, the camera won't have a problem finding a suitable speed, but problems arise when you use a wide depth of field without much available light, because a wide depth of field uses a small aperture (such as f16/22), which lets very little light into the lens. To compensate, the camera chooses a slower shutter speed to allow more light into the camera.

In low light, the camera will choose a shutter speed that is too slow for you to hold the camera by hand without causing blurriness. In these cases, the most common solution is to use a tripod. If you don't have a tripod with you, increase your ISO to compensate for the lack of light, which will then push up your shutter speed. However, the more you push your ISO, the more noise your image displays.