Is there a way to calculate field width from the mm of the lens?

Discussion in '35mm Cameras' started by BobFlint, Apr 12, 2006.

  1. BobFlint

    BobFlint Guest

    In other words, if I'm 12 feet from something and I want to have a 6 foot wide
    field of view, what mm lens would I use?

    Since I'm using a D70 I guess I'll have to figure with the cropping factor, no
    big deal...

    I want to get a wide fixed lens and there is a 24mm in the store, and I can
    order a 20mm if I want... for $100 more... I'm wondering how to calculate what
    the different view would be...

    I've been taking test pics with a zoom lens but that's tedious... some nice math
    charts would be nice!

    Thanks
     
    BobFlint, Apr 12, 2006
    #1
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  2. BobFlint

    Scott W Guest

    The D70 sensor is 23.7mm wide, so if you are 12 feet from a 6 foot wide
    traget you would need a lens that has a FL of 23.7mm * 12 / 6 or
    47.4mm.

    Scott
     
    Scott W, Apr 12, 2006
    #2
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  3. BobFlint

    Peter Chant Guest

    It's fairly simple, you need to know the sensor width. You can then
    calculate the field width using similar triangles.

    Pete
     
    Peter Chant, Apr 12, 2006
    #3
  4. BobFlint

    Matt Clara Guest

    Simpler yet, take a slide mount, use it to frame the shot you want, measure
    from the slide mount to your eye, the distance in millimeters will
    correspond to the lens you would use to frame the same shot. You can attach
    a bit of measuring tape to the slide mount to aid in quick measurment.
    Because the slide mount represents 35mm, you'll need to mask out part of the
    opening to correspond to the D70's sensor size.
     
    Matt Clara, Apr 12, 2006
    #4
  5. BobFlint

    Jim Guest

    Yes, it is just a matter of trigonometry.
    Nikon shows the angle of view of their lenses. These charts are really
    quite common.
    Jim
     
    Jim, Apr 12, 2006
    #5
  6. Using a 35 slide mount as described in another post is the simplest but
    if you have a calculator with you: f = focal length. M =
    magnification. For a format width, height, or diagonal of distance X,
    the angle of coverage along the width, height, or diagonal is
    2*ARCTAN( X / (2*f*(M+1))). At infinity the magnification M is 0 so
    the formula is 2*ARCTAN( X / 2*f ).
     
    bob.kirkpatrick, Apr 12, 2006
    #6
  7. BobFlint

    BobFlint Guest

    Thanks! That matches my test shot as well...
     
    BobFlint, Apr 13, 2006
    #7
  8. BobFlint

    BobFlint Guest


    As Spock would say... Fascinating!

    There's nothing like empirical engineering!

    thanks
     
    BobFlint, Apr 13, 2006
    #8
  9. BobFlint

    BobFlint Guest


    I figured that much...

    Why not?

    Maybe, but I haven't seen them... and they wouldn't apply to a D70...
     
    BobFlint, Apr 13, 2006
    #9
  10. BobFlint

    BobFlint Guest


    Thanks - I'll do a spreadsheet sometime...
     
    BobFlint, Apr 13, 2006
    #10
  11. BobFlint

    Jim Guest

    The last few full catalogs have a table which lists every Nikon lens. This
    list shows the angle of view for 35mm cameras and the APS-C digital cameras,
    The D70 is such a camera.
    You can also find such a list on the Nikon web site.
    Jim
     
    Jim, Apr 13, 2006
    #11
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