f/stops

Discussion in 'Miscellaneous Equipment' started by SLNestler, Jun 28, 2005.

  1. SLNestler

    SLNestler Member

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    Hi.
    Does anyone out there know what "f" stands for in f/stop?
    I saw it once in an obscure book, and can't find it again.
    It's one of the most used terms in photography, but I can't find its derivation again.
    I know it's a French word, but since my French vocabulary was learned from Miss Piggy, I'm stumped.
    Thanks.
    Steven
     
  2. VoidoidRamone

    VoidoidRamone Subscriber

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    I always thought the "f" stood for focal length
    -Grant
     
  3. glbeas

    glbeas Member

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    You'll find reference in past postings in the forums. It refers to the optical diameter of the aperture expressed as fraction of the focal length. As in an f/2 50mm lens has an aperture 25mm in diameter, a 100 mm f/2 has a 50mm diameter one. The reason for using this system is both f/2 lenses transmit the same amount of light even though the apertures are different sizes. Keeps life simple for the photog.
     
  4. Claire Senft

    Claire Senft Member

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    F stands for fractional.
     
  5. Ed Sukach

    Ed Sukach Member

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    "f" (lower case) is standard for "focal length". "f/stop" indicates an aperture diameter that is "focal length" divided by whatever denominator. With a focal length of 50 mm, the aperture diameter represented by f/2, given a 50mm lens, is 50mm/2, or 25mm.

    Note that "f" refers to the actual focal length at the moment, not necessarily at infinity. If a lens is extended to say 75mm for close focusing, the "f/stop" value in the above example changes to 75mm/25 (aperture diameter), or f/3.
     
  6. pelerin

    pelerin Member

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    I like Claire's explanation, but I think the the word you are thinking of is "fenetre" or window (here misspelled 'cause I am not savvy enough to get "^" to appear in the middle of the word). Similarly I was once told that it was derived from the latin word fenestra. ...if death by beheading is decapitation and death by being pitched out a window is defenestration, is the unconcious clipping of heads through poor framing deparallaxation?
    Celac.
     
  7. Helen B

    Helen B Member

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    I agree with Grant and Ed - f is 'focal length'. The denominator is the diameter of the entrance pupil.

    And is a decimetre something that's been dug out of a cemetery?

    Best,
    Helen
    PS ê might be Alt+0234?
     
  8. modafoto

    modafoto Subscriber

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    Hmmm...another "f" word :smile: