When you are shooting in Tv mode, your camera will often be set at its widest aperture to bring in as much light as possible through the lens. Using a very large aperture allows you to use a faster shutter speed and narrows your depth of field (Figure 6.6).
So when will you want to use the Av mode for action and sports? You already know that using the Tv mode allows you to choose your shutter speed, so if you need a specific and fast shutter speed, Tv mode is a good choice. But if you want to isolate your subject and blur the background by using a large aperture, then you will probably want to set your camera to Av. One benefit to using the Av mode with the aperture at its widest setting is that the camera will always use the fastest possible shutter speed depending on the available light in your environment.
You can also change the ISO quickly when shooting in the Av mode, just as you learned in the previous section. Just remember to keep an eye on the shutter speed— if it’s too slow, boost the ISO number to increase the sensitivity of the sensor and allow the use of faster shutter speeds.
One challenge you’ll face when using a wide-open aperture in action photography is that you need to be sure you maintain proper focus on your subject, because you have less wiggle room with a larger aperture than with a smaller one. You also want to be able to take several continuous photos of your subject to make sure you get the shot (“machine gun” style). With portrait and landscape photography, you can easily get away with One Shot AF (autofocus) and the Single shooting drive mode. But when you are trying to focus on something that is constantly moving, it’s much easier to use a focusing system that can track your subject. In the next section, I will discuss the 60D’s drive modes, focus modes, and the AF selection points you can use when photographing fast-moving subjects.