Photo Term Series #6: f-stop, f/stop or f-number
“the f-number (sometimes called focal ratio, f-ratio, or relative aperture[1]) of an optical system expresses the diameter of the entrance pupil in terms of the effective focal length of the lens. It is the quantitative measure of lens speed, an important concept in photography” – Wikipedia
In other words, the f-stop is the ratio of lens focal length to the effective aperture open diameter. Each f-stop step increment represents a doubling or halving of the lens aperture open area and thus the amount of light admitted into the lens
[wide open] 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 23, 32 [closed down, pinhole].
Note: f-stop values are a key reference in discussing Depth of Field (DOF).
(See Photo Term Series Post #7: Depth of Field (DOF))
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[...] The ratio of the lens focal length to the effective aperture provides the f/stop value. (see Photo Term Series Post #6: f-stop, f/stop or f-number) Bookmark to: One Response to ‘Photo Term Series Post #5: Aperture’ [...]
[...] Tilt-shift lenses are a specialized lenses that allows you to adjust the plane of focus by physically repositioning lens elements. This can result in sharper images and provide a means of gaining greater depth of field at lower f-stops. Unfortunately I don’t yet have a tilt-shift lens, but its a lens that I very much want to get. [...]
[...] Photographers often become frustrated because the tools at our disposal lack the ability to recreate the full range of light we inherently see. For film and digital alike, photographers think in terms of stops of light (referring to f/stop). It’s widely accepted that film has a dynamic range of 4-8 stops, digital sensors have a dynamic range of 10-14 stops and the human eye a dynamic range of 20-24 stops*. Note: *The fixed dynamic range of our retina is about 6 stops, but exposure is variably adjusted chemically and by our iris as it contracts and expands. [...]