Aperture priority, often abbreviatedA orAv (foraperture value) on a cameramode dial, is amode on some cameras that allows the user to set a specificaperture value (f-number) while the camera selects ashutter speed to match it that will result in properexposure based on the lighting conditions as measured by the camera'slight meter. 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, orprogram mode where the camera selects both.[1]
As an image'sdepth 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 inlandscape 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 ahigh f-number, e.g. f/16 or f/22) is necessary. Aperture priority mode also finds use inportrait photography, where a wide aperture (identified by alow 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.[1]
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, so that the camera will select a slow shutter speed (to allow a sufficient amount of light to reach thefilm orsensor for proper exposure), thereby causing the water toblur through the frame.[2] 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.
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