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  1. #1
    Stephen Benskin's Avatar
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    Hiding in Plain Sight

    The Kodak Graphic Representation of Typical Photographic Tone Reproduction diagram is fairly well known. Iíve always found it to be a excellent illustration of the photographic process, but it contains a lot of information, and sometimes important details can get overlooked. There's a concept hiding in plain sight.

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    Looking at the diagram, it has a 7 stop range for the subject (log subject luminance range 2.10). And it has a negative density range of 1.05 when the film is developed to a CI of 0.56. According to the equation for slope, Rise/Run, that should be 1.05 / 2.10 = 0.50 and not 0.56. By the looks of things, 0.56 would be over-processing it a bit.

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    Flare?

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    To my eye, what looks to be hidden in plain sight is the resemblance of the shape of the chart to a large format lens. As seen from the side.
    "Only dead fish follow the stream"

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    Bill Burk's Avatar
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    It's flare all right, the CI was calculated using the image at the film plane which includes flare: 1.05 / 1.85 is about 0.56

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    Interesting also that the dotted line representing 18% reflectance is at the high side of middle gray. This bolsters a post from a few weeks back that 12% reflectance value is perhaps a better value for calibrating Zone V than 18%. Fascinating. I've known about that chart for 20 or more years and never noticed.

    Peter Gomena

  6. #6
    Stephen Benskin's Avatar
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    Quote Originally Posted by pgomena View Post
    Interesting also that the dotted line representing 18% reflectance is at the high side of middle gray. This bolsters a post from a few weeks back that 12% reflectance value is perhaps a better value for calibrating Zone V than 18%. Fascinating. I've known about that chart for 20 or more years and never noticed.
    This kind of thing happens to me all the time. Once something is pointed out, I keep seeing it everywhere. Every once in a while, I'll go back through a book and suddenly see all these references that I hadn't noticed the last dozen or so times I had read it. This happened recently when doing the speed/exposure meter relationship thread. I was reviewing a few papers and a couple chapters and I kept seeing all these references to the relationship. And not long ago, I kept running into the phrase "good correlation" between the fractional gradient method and the fixed density film speed. It was used so often in so many sources that it almost seemed like some kind of well known code for something. I was surprised to see it in so often with what I had read and re-read so many times without it ever registering before.

  7. #7
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Flare?
    Quote Originally Posted by Bill Burk View Post
    It's flare all right, the CI was calculated using the image at the film plane which includes flare: 1.05 / 1.85 is about 0.56
    Fine, maybe it wasnít hiding very well. But letís take a look at the value of the negative density range Ė 1.05. That falls right in the center of the grade 2 paper LER range.

    Kodak has a negative density range of 1.05 using a CI of 0.56. This diagram has been frequently reproduced. Kodakís technical data sheets also use 1.05 and CI 0.56 (more recently CI 0.58). Many books and publications have this value. Many books show how flare reduces the sceneís apparent luminance range within the camera. How a 7 1/3 stop scene is reduced to a 6 1/3 or even 6 stop exposure range at the film plane. The log exposure ranges for various grades of paper are also reproduced in books and publications. A grade 2 is generally listed as being from an LER of 0.95 to 1.14. That fits in perfectly with the 1.05 negative density range.

    These numbers are reproduced over the place. Itís hard to miss them, so why do people still insist on negative density ranges of 1.20 to 1.35? Shouldnít the difference between the two sets of numbers at least create some questioning in peopleís minds? The information is right there. How can it be missed? I thought it all had to be hiding in plain sight. Maybe by pointing out these values, they will suddenly appear and become noticeable in all those books and publications.
    Last edited by Stephen Benskin; 01-20-2012 at 08:38 PM. Click to view previous post history.

  8. #8
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    These numbers are reproduced over the place. Itís hard to miss them, so why do people still insist on negative density ranges of 1.20 to 1.35?
    Saw this again today and right about the time I was going to say - no don't develop to 1.2 - I realized you are supposed to overrun by about 0.1

    ---
    Guess why? I'm thinking flare again.
    ---
    I think enlarger flare is going to take that 0.15 off the negative density range and leave you with 1.05 on the paper.

  9. #9
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Saw this again today and right about the time I was going to say - no don't develop to 1.2 - I realized you are supposed to overrun by about 0.1

    ---
    Guess why? I'm thinking flare again.
    ---
    I think enlarger flare is going to take that 0.15 off the negative density range and leave you with 1.05 on the paper.
    Flare does play a factor in printing, but I believe the LER to negative density range is off set by the Callier coefficient.

    The answer is flare, but it's still the camera flare. The short answer is:

    2.10*0.56 = 1.17
    2.10*0.58 = 1.22

    2.20*0.56 = 1.23
    2.20*0.58 = 1.28

  10. #10
    Stephen Benskin's Avatar
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    Itís a simple case of misinterpreting the data. The exposure range is smaller than the scene luminance range do to the effects of flare. We know that flare affects the shadows to a greater proportion than the highlights. Flare reduces the exposure range between the metered exposure and the shadow exposure. It shifts the shadow exposure toward the metered exposure.

    But when testing for negative contrast, it is common to use the speed point as the base point to calculate the film gradient. In the example below, the film is processed to a CI 0.60 which is slightly higher than the standard model, but fits the ideal Zone System model (CI 0.595).

    Click image for larger version. 

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    The difference between the two values for the negative density range of 1.06 and 1.27 is the difference in the range from the shadow to the highlight exposure. One uses a seven stop scene luminance range and the other a 7 1/3 stop scene luminance range to begin with, but factors in a 1 1/3 stop flare factor making for an exposure range of 1.80. (To simplify the comparison, you can also think of it as a 7 stop scene luminance range with one stop flare.)

    The difference in ranges come from measuring different points on the same curve. But conceptually, one is recognizing the difference between the scene luminance range and the camera exposure range and one is not.
    Last edited by Stephen Benskin; 01-21-2012 at 10:07 AM. Click to view previous post history.

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