When the depth of field is most important, photographers choose aperture priority to make quick changes in the f-stop. This setting allows maximum focus for landscapes, for example, and out-of-focus backgrounds that work well with portraits. When shutter speed is most important, they chose shutter priority — for action shots, for example. The operation of both modes is very similar.

After selecting the aperture-priority setting, the photographer pushes a button mounted on the camera body (in many camera designs). By pushing the button, the photographer changes the aperture either up or down. The LCD readout informs the photographer and keeps her on top of and in control of the changes she is making. However, every change in f-stop causes a corresponding change in shutter speed, so the photographer needs to keep an eye on that as well. If the shutter speed gets too slow, for example, the picture will be blurred and all that wonderful sharply focused depth of field will be lost in the blur of camera shake.

The automatic setting of the aperture makes the background in this photo too sharp.

Choosing a minimum aperture in aperture priority throws the background out of focus, which makes the banana stand out more in the photo.

With most digital cameras it will be very hard to judge the depth of field before taking the picture. The preview image on the LCD monitor is usually the view of the scene at the largest lens opening (and least depth of field). However, after taking the shot, the photographer can view the resulting shot and use the LCD review and the LCD zoom review feature to judge the quality of the focus. Some very high-end cameras offer a depth of field preview, but this is not a common feature.

Setting the shutter priority setting is similar to setting the aperture priority. After selecting the shutter priority setting, the photographer pushes a button mounted on the camera body (in many camera designs). This changes the shutter speed to faster or slower. The LCD readout informs the photographer and keeps her on top of and in control of the changes she is making. However, she needs to consider how the change in shutter speed will affect the corresponding change in f-stop.

The autoexposure setting chose a shutter speed that was too slow, causing the head of the cat to blur.

A faster shutter speed, in shutter priority mode, allowed a sharp picture of this cat.

When the photographer controls shutter speed, she can shoot fast-action situations so that the pictures are sharp and clear or use a slower speed to give the action a slightly blurred but dynamic look. She can also use very fast speeds to make waves on a river look like hard ridges of ice or choose a slow shutter speed to make the same river look like soft clouds of foam.