What is Aperture Priority?

In a nutshell, Aperture Priority is a setting on many cameras (both digital and film) where the user sets the aperture and the camera then adjusts the shutter speed automatically to get a correct exposure.

On most cameras, Aperture Priority is enabled by putting the main control dial in "A" (Nikon) or in "Av" (Canon), which stands for "Aperture value".

How does Aperture Priority work?

Once you set the camera to Aperture Priority and have chosen the aperture you want, the camera will use its internal light meter to determine the appropriate shutter speed required for a correct exposure given the available light. So, the shutter speed will be variable but the aperture will remain constant on what you've set the camera to. In other words, it's the reverse of Shutter Priority.

Why is Aperture Priority important?

Because it allows you, the photographer, to decide what aperture is needed to get the effect you’re after. This mode is most useful when depth of field is important, either the existence or lack of it. For example, if you’re shooting a portrait and want enough depth of field to blur the background while maintaining the subject sharp, you might want to set your camera in Aperture Priority and select an aperture of, say F2.8, and let the camera worry about the shutter speed required to give you a well exposed photograph. On the other hand, if you’re shooting a landscape and want everything in focus, you may select an aperture of, say F16, and just shoot away without worrying about the shutter speed.

Same caveat as with Shutter Priority applies here. Remember to check that there is enough light for the camera to actually be able to give you a correct exposure or viceversa. You can learn more about aperture, shutter speeds, and exposure in other articles.

As a final note, this is the mode I personally use most of the time. Actually, unless I need to use Manual mode for a specific reason, I’ll almost always use Aperture Priority.