Using Aperture Priority (Av) Mode to Isolate Your Subject

When using Tv mode with fast shutter speeds, you will often find that you are shooting with a wide-open aperture to allow enough light to hit the sensor (Figure 4.6). As you recall from Chapter 3, a large aperture (f/2.8, for example) allows the subject to stand out from the background, naturally drawing the point of focus to your subject.

Figure 4.6. Because I used a large aperture, the pelican stands out from the tree in the background.

So when is it appropriate to use Av mode for action and sports photography? Tv mode is great when you want to use a specific shutter speed, but it doesn’t guarantee that a specific aperture is selected along with it. So when you want to guarantee the use of a large aperture to isolate your subject, you will want to use Av mode. Since the camera is always trying to balance the amount of light hitting the sensor on your camera, choosing a wide-open aperture will force the camera to pick a fast shutter speed to balance out the amount of light coming through the lens. This works best when you have a lot of light in your scene.

Don’t forget that you can also increase the shutter speed in Av mode by adjusting the ISO. If you find that the shutter speed chosen for the aperture you selected is not fast enough, boost the ISO number to increase the sensitivity of the sensor, which in turn allows for a faster shutter speed.