Also Known As: F/Number, F-Stop, Effect Aperture, Relative Aperture. A measure of the width of the opening allowing light to enter a camera. The apparent diameter of a lens viewed from the position of the object against a diffusely illuminated background is called the "effect aperture". The ratio of focal length of a lens to its "effective aperture" for an object located at infinity is called the "relative aperture", or "f/number". Larger apertures allow more light to enter a camera, hence darker scenes can be recorded. Conversely, smaller apertures allow less light to enter, but have the advantage of creating a large depth of field. See also shutter speed.