ABSTRACT
The amount of light that reaches the film or digital sensor-and therefore the exposure-is determined by the aperture and the shutter speed. The maximum aperture of a lens is frequently referred to as the “speed” of the lens, and large aperture lenses are known as “fast” lenses. The aperture is determined by the size of the diaphragm opening, with a low number, such as f 2.8, indicating a larger opening. You reduce the amount of light reaching the image plane by setting the aperture to a higher number, such as f/11. A change in aperture from one setting to the next either doubles or halves the amount of light reaching the image plane.
