20D 1 1/3 Stops Slower Than 5d?

Discussion in 'Digital Photography' started by David, Apr 24, 2006.

  1. David

    David Guest

    I read somewhere that a EF 24-105mm f/4L IS USM lens acts 1 1/3 stops faster
    on a 5D to a 20D. That means it's equivalent to an f2.5 lens on a 20D.

    I don't understand. Can someone please explain what this is about?
    David, Apr 24, 2006
    #1
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  2. David

    Prometheus Guest

    In article <>, David <>
    writes
    >I read somewhere that a EF 24-105mm f/4L IS USM lens acts 1 1/3 stops faster
    >on a 5D to a 20D. That means it's equivalent to an f2.5 lens on a 20D.
    >
    >I don't understand. Can someone please explain what this is about?


    This sounds like a depth of field effect and not the amount of light
    passed through which depends on the f/ number, not what comes after the
    lens. The smaller sensor requires a smaller CoC which means setting a
    smaller aperture.

    --
    Ian G8ILZ
    Prometheus, Apr 25, 2006
    #2
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  3. "David" <> wrote in message
    news:...
    >I read somewhere that a EF 24-105mm f/4L IS USM lens acts 1 1/3 stops
    >faster
    > on a 5D to a 20D. That means it's equivalent to an f2.5 lens on a 20D.
    >
    > I don't understand. Can someone please explain what this is about?


    There are a variety of theories here.

    http://www.ddisoftware.com/20d-5d/#nsprof

    This shows that the 5D noise at any given ISO is about the same or better
    than the 20D noise at one stop slower (half the ISO). At ISO 400, the 5D is
    very close to the 20D at ISO 100.

    So you can shoot at ISO 400 on the 5D and get very similar image quality to
    any other dSLR at ISO 100.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Apr 25, 2006
    #3
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