A digital camera may have manual as well as semi-automatic modes that let you control aperture and shutter speed. Together, aperture and shutter speed determine how a photo is exposed.

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 used when you want 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), 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.