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Aperture priority, often abbreviated ''A'' or ''Av'' (for aperture value) on a camera mode dial, is a mode on some cameras that allows the user to set a specific
Aperture priority, often abbreviated ''A'' or ''Av'' (for aperture value) on a camera mode dial, is a mode on some cameras that allows the user to set a specific aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An ...
value (f-number
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill Pro ...
) while the camera selects a shutter speed to match it that will result in proper exposure based on the lighting conditions as measured by the camera's light meter
A light meter is a device used to measure the amount of light. In photography, a light meter (more correctly an exposure meter) is used to determine the proper exposure (photography), exposure for a photograph. The meter will include either a Di ...
. This is different from manual mode, where the user must decide both values, shutter priority where the user picks a shutter speed with the camera selecting an appropriate aperture, or program mode where the camera selects both.
Uses
Depth of field
As an image's depth of field is inversely proportional to the size of the lens's aperture, aperture priority mode is often used to allow the photographer to control the focus of objects in the frame. Aperture priority is therefore useful in landscape photography, for example, where it may be desired that objects in foreground, middle distance, and background all be rendered crisply, while shutter speed is immaterial. To obtain this large depth of field, a narrow aperture (identified by a ''high'' f-number, e.g. f/16 or f/22) is necessary. Aperture priority mode also finds use inportrait photography
Portrait photography, or portraiture, is a type of photography aimed toward capturing the personality of a person or group of people by using effective lighting, backdrops, and poses. A portrait photograph may be artistic or clinical. Frequentl ...
, where a wide aperture (identified by a ''low'' number, e.g. f/1.4 or f/2.8) and therefore smaller depth of field may be desired to throw the background out of focus and make it less distracting.
Shutter speed
Another common use of aperture priority mode is to indirectly affect shutter speed for a desired effect. In landscape photography, a user might select a small aperture when photographing awaterfall
A waterfall is a point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf.
Waterfalls can be formed in severa ...
, so that the camera will select a slow shutter speed (to allow a sufficient amount of light to reach the film or sensor for proper exposure), thereby causing the water to blur through the frame. At the contrary, a larger aperture allows to shorten the shutter speed reducing the hand jitter by taking a picture without a tripod or, in alternative, a lower ISO to enhance the image quality by reducing the noise.
When shooting a portrait in dim lighting, the photographer might choose to open the lens to its maximum aperture in hopes of getting enough light for a good exposure while maintaining the shortest possible shutter speed to reduce blur.
See also
*Digital camera modes
Most digital cameras support the ability to choose among a number of configurations, or ''modes'', for use in various situations. Professional DSLR cameras provide several manual modes; consumer point-and-shoot cameras emphasize automatic modes; ...
* Shutter priority
References
Camera features {{Photo-stub