f-number
Sign in to saveright|thumb|320px|Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.
Article
24 sectionsContents
- Notation
- Conventional scales
- Fractional stops
- Standard full-stop f-number scale
- Typical one-half-stop f-number scale
- Typical one-third-stop f-number scale
- Typical one-quarter-stop f-number scale
- Effect on exposure
- Camera equation
- T-stop
- H-stop
- ASA/ISO numbers
- Gain
- Sunny 16 rule
- Effects on image sharpness
- Human eye
- {{anchor|Focal ratio}}Focal ratio in telescopes
- History
- Origins of relative aperture
- Aperture numbering systems
- Typographical standardization
- See also
- References
- External links
right|thumb|320px|Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.
An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is defined as the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture"). The f-number is also known as the focal ratio, f-ratio, or f-stop, and it is key in determining the depth of field, diffraction, and exposure of a photograph. The f-number is dimensionless and is usually expressed using a lower-case hooked f with the format N, where N is the f-number.