Definition of f-number in English:

f-number

noun

Photography
  • The ratio of the focal length of a camera lens to the diameter of the aperture being used for a particular shot (e.g., f8, indicating that the focal length is eight times the diameter)

    F
    • ‘All these f-numbers, focal lengths, film speeds and apertures are actually really simple to get to grips with once you understand how they relate to each other and to the finished picture.’
    • ‘The f-numbers marked on a lens are only truly accurate when the lens is focused at infinity.’
    • ‘So if you want to have that window frame, the couple, and the envelope all in focus, you need a narrow aperture, and so a large f-number, such as f22.’
    • ‘The configuration offers the advantage of high image quality, low distortion, and low f-number, making it ideal for spectral imaging.’
    • ‘The higher f-numbers mean the diameter of the lens can be smaller, so the lens, using only 20% to 25% as much material, will cost less and weigh less.’

Origin

Early 20th century: from f (denoting the focal length) and number.

Pronunciation:

f-number

/ˈef ˌnəmbər/