Circle of confusion for nikons dof scales

Discussion in 'Nikon' started by Marc Wossner, May 27, 2007.

  1. Marc Wossner

    Marc Wossner Guest

    Hi,

    calculating the circle of confusion for the depth of field scales of
    my nikkor lenses with the equation from norman korens website (http://
    www.normankoren.com/Tutorials/MTF6.html#DOFscale - C = f^2 / Nmax * (s-
    f)) I found that they differ throughout the focal lenghts:

    f/3,5 18 mm = 0,044 mm
    f/2,8 24 mm = 0,069 mm
    f/2,8 28 mm = 0,037 mm

    I´m quite astonished in finding a) such huge differences and b) values
    so far apart from the industrie standard criterion of 0,032 mm. Can
    anyone confirm those findings?

    Best regards!
    Marc
     
    Marc Wossner, May 27, 2007
    #1
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  2. Marc Wossner

    Alan Browne Guest

    The DoF markings on a lens are for guidance, not absolute results.

    If you "lock" some variables then other variables like CoC have to
    change. But that's probably not what you're looking for.

    The "standard" is typically based on a print size of 8x10 (inches)
    viewed at about 12 - 18" away, and this what is reflected in the DOF
    scales on 35mm and AFAIK most (all?) MF lenses.

    The CoC that you "want" is properly driven by the enlargement ratio from
    the film to the print. The greater the enlargement ratio, the smaller
    CoC you will want in which case the DOF markings on the lens are not
    tight enough. ... unless the larger print is viewed even further away,
    in which case it's a wash.
    The industry standard CoC for 35mm is actually closer to 0.025mm for the
    "reference" print size.

    Again, CoC should be driven by your preferred print size not the lens
    markings ... unless of course you always print at about 8x10".

    Cheers,
    Alan.
     
    Alan Browne, May 27, 2007
    #2
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  3. Marc Wossner

    Paul Furman Guest

    This is three different lenses? The 2.8/24 just isn't sharp? Or I guess
    it's just different people designing the DOF scales over the years...
    also many lenses are not exactly the focal length they state, the stated
    length is often just a rounded number for simple labelling.
     
    Paul Furman, May 27, 2007
    #3
  4. Marc Wossner

    Marc Wossner Guest

    On 27 Mai, 19:07, Alan Browne <>
    wrote:

    You´re absolutely right and I wasn´t looking for that.
    I was just trying to figure out the value the dof scales that my
    lenses rely on
    to be able to set aperture right for my desire.

    Best,
    Marc
     
    Marc Wossner, May 27, 2007
    #4
  5. Marc Wossner

    Marc Wossner Guest

    Nothing to complain about that.
    But it´s one manufacturer and therefore I was expecting one value.
    You mean the rounding can change the value so far off?

    Best,
    Marc
     
    Marc Wossner, May 27, 2007
    #5
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