| 单词 | f-number |
| 释义 | f-number /ef"num'beuhr/, n. Optics, Photog. a number corresponding to the ratio of the focal length to the diameter of a lens system, esp. a camera lens. In f/ 1.4, 1.4 is the f-number and signifies that the focal length of the lens is 1.4 times as great as the diameter. Abbr.: f/, f/, f, f: Also, f number. Also called focal ratio, speed, stop number. Cf. relative aperture. [1890-95] |
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