A majority of modern film cameras have a special feature on the shutter speed dial called aperture priority, denoted with an ‘A’ on the dial. Typically in film photography the photographer must manually choose both the aperture and shutter speed for a proper exposure using a light meter or other method. With aperture priority the user simply chooses an aperture setting and the camera automatically adjusts the shutter speed, ensuring proper exposure.
Aperture Priority in Depth of Field
As the aperture controls depth of field for the photograph, aperture priority is no different. But now, instead of worrying about the shutter speed setting, the photographer simply needs to decide how large the aperture opening will be and how much depth of field is desired. Film photography dictates that a small aperture opening results in great depth of field where everything is in focus and a large aperture opening results in shallow depth of field where only the point of interest is in focus. In between are, of course, variable amounts of great or shallow depth of field.
Another use of aperture priority in film photography is to force the camera to dictate a shutter speed without risking proper exposure. This is particularly helpful in bright or low-light situations. In a bright scene, the aperture should be small to avoid overexposure and highlights, forcing your camera to use a slower shutter speed. Alternatively, in a low-light situation, the aperture should be large to allow in more light, forcing the camera to use a faster shutter speed and minimize blur. Because the camera is automatically compensating the shutter speed, a balanced exposure may often results in these situations.
Shutter Speed Priority
While aperture priority causes the camera to automatically register the correct shutter speed, some cameras may also have shutter priority. Shutter priority is the inverse of aperture priority where the user sets the shutter speed and the camera automatically adjust the aperture. Read more about this film photography technique in the shutter priority page.