A camera's exposure modes determine how much control you have over two critical exposure settings — aperture and shutter speed.
- The aperture is the opening created by a set of overlapping metal blades, known as the diaphragm, inside a photographic lens. This opening controls the volume of light of the photo. Aperture is measured in f-stops, which affects the depth of field and how much light passes through the opening.
- The shutter is a mechanism that opens and closes to admit light into a camera for a measured length of time. It can operate at different speeds or durations, ranging from fast (e.g., a fraction of a second) to long (e.g., whole seconds, minutes or hours). The shutter speed you choose will affect your exposure and have a direct effect on stopping (i.e., freezing) or blurring motion.
On a camera, you can choose the full manual (M) mode, or one of the three semi-automatic modes: aperture priority auto (A), shutter priority auto (S) and programmed auto (P). These semi-automatic modes allow you to get some exposure assistance from the camera.
Explore the exposure mode settings below and how they can help you capture the best image.
Exposure Mode Settings
In manual mode, you control both aperture and shutter speed. Use the exposure meter to help you adjust the aperture and shutter speed for balanced exposure. In this mode, it's important to understand how lighting levels affect exposure. Manual mode gives you complete control over your camera and the outcome of the image.
The photograph below of the U.S. Air Force Honor Guard Drill Team at attention during a parade demonstrates how manual mode can be used to take a successful image by giving you control to adjust for the scene.
In aperture priority auto mode, you control the aperture and the camera automatically adjusts the shutter speed to produce balanced exposure. This mode is ideal for portraits or macro photography, where capturing the motion of the subject is not as important as controlling the depth of field in the image.
The photograph below of Air Force Staff Sgt. Garion Reddick straining during the flex arm hang portion hang test below how the aperture priority auto mode is ideal for taking a close-up.
In shutter priority auto mode, you set the shutter speed and the camera automatically adjusts the aperture for a balanced exposure. This mode is preferred for capturing sports or other moving subjects and uncontrolled action because it gives you direct control over shutter speed.
The photograph below of Air Force Academy graduates tossing their hats with Thunderbirds soaring overhead shows how the shutter priority auto mode is the best choice for capturing an uncontrolled action shot.
In programmed auto mode, the camera meters the scene and selects the aperture and shutter speed for balanced exposure. You can choose from different aperture and shutter speed combinations to vary the results. This is the recommended mode for snapshots and still portrait settings.
The photograph below of a service member embracing his family during a homecoming shows how the programmed auto mode can be used to take a snapshot.an choose from different aperture and shutter speed combinations to vary the results. This is the recommended mode for snapshots and still portrait settings.