EN: F/number or f/stop
The numerical expression of the relative aperture of a lens. Each f/number is 1.4 times larger than the preceding one, and each number indicates a halving or doubling of the amount of light allowed to pass through the lens.
The lens focal length divided by effective diameter of the aperture gives the f/number that s used to indicate the aperture value. Each full f/number, also called a stop or f-stop, halves or doubles image brightness and some lenses can also be controlled in half or third steps. The most common f/numbers are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and 22. They are usually preceded by an f. The larger the f-number, the smaller the lens opening. In the aforementioned series of numbers, f/1.4 is the largest opening and f/22 the smallest. The smaller stops (larger f numbers) give the greater depth of field in a photograph, and vice versa. .
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