ABSTRACT
The amount of light reaching a photographic emulsion must be controlled in order to ensure the right exposure. Exposing the film in the camera is typically done with a combination of lens aperture and shutter timing. The lens aperture, also called ‘f/stop’, controls the light intensity, and the shutter timing, also called ‘speed’, controls the duration of the exposure. The f/stop settings are designed to either half or double the light intensity. The shutter speed settings are designed to either half or double the exposure duration. This is accomplished by following a geometric series for both aperture and time. The ‘film exposure control’ table in fig.2 shows an example of typical settings used in modern cameras and lenses. Therefore, an f/stop adjustment in one direction can be offset by a shutter speed adjustment in the opposite direction. Experienced photographers are very comfortable with this convenient method of film exposure control and refer to both, aperture and shutter settings, as f/stops or simply, ‘stops’.
