Wikipedia:Picture of the day/August 4, 2005
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In photography, the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. The diaphragm aperture diameter is proportional to the focal length divided by the f-number. The greater the f-number, the greater the depth of field and the less light per unit area reaches the focal plane. The standard sequence of f-stops on a camera lens represent a halving of the light intensity at each step. Photo credit: MarkSweep |