The faster the shutter speed, the larger the opening of the lens (ie. smaller aperture number). Conversely, the slower the shutter speed, the smaller the lens opening.
Aperture-priority (AV) mode
When using aperture-priority, also known as Av mode, you manually select the aperture and the camera automatically sets the shutter speed.
The aperture is the opening in a lens that admits light onto the camera sensor and is varied by changing the size of the opening. It’s diameter is stated as an f-stop.
Aperture-priority mode is often used to control depth-of-field, the area a photo is sharp in front and back of where you focus on the main subject.
Shutter-priority (TV*) mode
Shutter speed relates to how long the camera’s shutter stays open after you depress the shutter-release button. Shutter speed is measured in seconds, such as 1/125th. A slow shutter speed produces a longer exposure time.
For shutter-priority mode (Tv), you select the shutter speed and the aperture adjusts automatically. Use shutter-priority mode when you want to control action in a photo either to freeze the action of fast moving subjects or to create a sense of movement, such as the movement of a cascading waterfall.
See our Shutter Speed Chart to learn to learn the effects of using different shutter speeds.