Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)

Discussion in 'Darkroom Developing and Printing' started by Steven Woody, Jan 14, 2007.

  1. Steven Woody

    Steven Woody Guest

    in Adams's book 'Negative', page 66, he showed a Exposure Formula:

    " to use the exposure formula, take the film speed number ( on the ASA
    scale ) and determine its approximate square root. This number is
    remembered as the key stop for that firm. for example, a film rated as
    ASA 125 has a key stop of f/11. at the key stop, the correct shutter
    speed in seconds to expose a given luminace on Zone V is the reciprocal
    of the luminace expressed in c/ft^2. thus for a sureface that measure
    60c/ft^2, we would use a shutter speed of 1/60 second at the key stop."

    but if using the APEX ( any one heard that? ), since Av + Tv = Bv +
    Sv, where Sv ( 125 ASA ) = 5.4, Bv ( 60c/ft^2 ) = 3.3, Av ( f/11 ) = 7,
    so Tv = 5.4 + 3.3 - 7 = 1.7 which is about 1/4 second.

    what's the wrong? thanks.

    -
    woody
     
    Steven Woody, Jan 14, 2007
    #1
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  2. Steven Woody

    JJ Guest

    It is more clear if you graph it out but it is still unnecessary to go
    to lengths to understand it. It is an approach and not the ultimate
    method. Adams still dodged, burned and bleached his way to happiness.

    Learn to expose for significant shadows, develop for highlights and be
    happy.
     
    JJ, Jan 14, 2007
    #2
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  3. It is more clear if you graph it out but it is still unnecessary to go
    to lengths to understand it. It is an approach and not the ultimate
    method. Adams still dodged, burned and bleached his way to happiness.

    Learn to expose for significant shadows, develop for highlights and be
    happy.[/QUOTE]

    & use a light meter.
     
    Gregory Blank, Jan 14, 2007
    #3
  4. Steven Woody

    Steven Woody Guest

    [/QUOTE]

    i just wonder, in this exposure, which one is wrong, Adams or APEX ?

    -
    woody
     
    Steven Woody, Jan 15, 2007
    #4
  5. Steven Woody

    Peter Irwin Guest


    60 candles per square foot is a brightness level of around 7.5

    That brings your total to 5.9 or very nearly 1/60th of a second.

    I think you looked up an incorrect table for brighness.
    In the Focal enclclopedia a bv of 7 is 45 canles/ ft^2
    and a Bv of 8 is 90 candles/ft^2.

    Peter.
     
    Peter Irwin, Jan 15, 2007
    #5
  6. Steven Woody

    JJ Guest

    & use a light meter.[/QUOTE]

    Uh, yeah, and a lightmeter.

    and World Peace!
     
    JJ, Jan 15, 2007
    #6
  7. Steven Woody

    Steven Woody Guest

    thank you. after read you post and did a research on the net, i can now
    draw a conclusion that,

    1, what adam mentioned 60c/ft^2 is a brightness of the scene. 60c/ft^2
    brightness equals to a Bv value of 7.56 ( you are right ).

    2, what i previously methioned Bv=3.3 for 60/ft^2 is from a table that
    actually list incident light values, which should be Iv instead of Bv.

    thank you very much!.

    -
    woody
     
    Steven Woody, Jan 15, 2007
    #7
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