Field of view - need help with the math

Discussion in 'Digital Photography' started by Peabody, Nov 13, 2011.

  1. Peabody

    Peabody Guest

    I have an old Kodak Medalist film camera that I want to shoot a few
    rolls with. It has a 100mm lens, and uses 120 film (actually 620)
    and gets 8 exposures per roll. So I think that's what's called the
    6x9 frame size, which is actually 56 x 84mm.

    I want to know what lens focal length on my Canon crop sensor
    camera would give the same field of view as the Kodak. That's a
    14.8 x 22.2mm sensor.

    Is it 26.4mm? Based on just eyeballing the viewfinders, using the
    kit lens on the Canon, that appears to be about right.
    Peabody, Nov 13, 2011
    #1
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  2. Peabody

    Bruce Guest

    Peabody <> wrote:

    >I have an old Kodak Medalist film camera that I want to shoot a few
    >rolls with. It has a 100mm lens, and uses 120 film (actually 620)
    >and gets 8 exposures per roll. So I think that's what's called the
    >6x9 frame size, which is actually 56 x 84mm.
    >
    >I want to know what lens focal length on my Canon crop sensor
    >camera would give the same field of view as the Kodak. That's a
    >14.8 x 22.2mm sensor.
    >
    >Is it 26.4mm? Based on just eyeballing the viewfinders, using the
    >kit lens on the Canon, that appears to be about right.



    The diagonal of a 56 x 84mm "sensor" is 100mm. The lens on your
    Medalist therefore has a focal length equal to the diagonal.

    The diagonal of a 14.8 x 22.2mm sensor is 26.7mm. So to get the same
    angle of view as the Medalist, you would need to choose a focal length
    that is equal to the diagonal. So the answer is 26.7mm.
    Bruce, Nov 13, 2011
    #2
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  3. Peabody

    dj_nme Guest

    On 13/11/2011 3:27 PM, Peabody wrote:
    > I have an old Kodak Medalist film camera that I want to shoot a few
    > rolls with. It has a 100mm lens, and uses 120 film (actually 620)
    > and gets 8 exposures per roll. So I think that's what's called the
    > 6x9 frame size, which is actually 56 x 84mm.
    >
    > I want to know what lens focal length on my Canon crop sensor
    > camera would give the same field of view as the Kodak. That's a
    > 14.8 x 22.2mm sensor.
    >
    > Is it 26.4mm? Based on just eyeballing the viewfinders, using the
    > kit lens on the Canon, that appears to be about right.
    >


    That sounds about right.
    100mm lens on a 6x9 camera is a "normal" lens (roughly equal to the
    diagonal of the film frame), just like a 50mm lens is on a 35mm camera.
    Doing the math with a crop factor of 1.6 for the Canon camera, 31.25mm
    would be exactly spot-on.
    Any focal length from 28mm to 35mm would be close enough, really.

    If you want to be ultra finicky about the correct length of a normal
    lens for 35mm, then you'd use 43.5mm on a 24x36mm camera and 27.2mm on
    1.6 crop factor camera.
    dj_nme, Nov 13, 2011
    #3
  4. In article <>, Bruce
    <> writes
    >Peabody <> wrote:
    >
    >>I have an old Kodak Medalist film camera that I want to shoot a few
    >>rolls with. It has a 100mm lens, and uses 120 film (actually 620)
    >>and gets 8 exposures per roll. So I think that's what's called the
    >>6x9 frame size, which is actually 56 x 84mm.
    >>
    >>I want to know what lens focal length on my Canon crop sensor
    >>camera would give the same field of view as the Kodak. That's a
    >>14.8 x 22.2mm sensor.
    >>
    >>Is it 26.4mm? Based on just eyeballing the viewfinders, using the
    >>kit lens on the Canon, that appears to be about right.

    >
    >
    >The diagonal of a 56 x 84mm "sensor" is 100mm.

    Not quite.

    >The lens on your
    >Medalist therefore has a focal length equal to the diagonal.
    >
    >The diagonal of a 14.8 x 22.2mm sensor is 26.7mm.

    Not quite.

    >So to get the same
    >angle of view as the Medalist, you would need to choose a focal length
    >that is equal to the diagonal. So the answer is 26.7mm.
    >

    If you are going to dispute Peabody's figure by little over 1% then you
    need to ensure that your own figures, and intermediate terms, are at
    least that precise - your first certainly isn't. Because of that, your
    answer is about 1% too high. So Peabody's own figure of 26.4mm is more
    accurate.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
    Kennedy McEwen, Nov 16, 2011
    #4
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