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  1. #1

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    Kodak Characteristic Curve - Log H Ref equals middle gray?

    Can anyone please explain me the value of Log H Ref given in most of Kodak Tech. Pub. Characteritic Curves? E.g. Ektar 100 E-4046 curve gives a Log H Ref of -0.84. Is it middle gray when shooting at box speed? Isn't middle gray normally placed at log 0?
    Compared to E-4040 Log H Ref -1.14 the Portra 160 VC seems to handle an enormous overexposure of nearly 7 stops.

  2. #2
    markbarendt's Avatar
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    Old thread old unanswered thread, but I was searching for the same answer this morning.

    Found this: http://motion.kodak.com/motion/uploa...y_workbook.pdf

    Page 6 seems to have the answer.

    Log H seems to be defined as "Exposure", I'm going to make the assumption that this essetially means "the camera setting". That seems to fit the curve, leaving room for about 3-4 stops down to the toe.

    Portra 160 http://www.kodak.com/global/en/profe...4051/e4051.pdf

    Portra 400 http://www.kodak.com/global/en/profe...4050/e4050.pdf

    I checked the TMax tech pub and it lacks the reference point.

    http://www.kodak.com/global/en/profe...4016/f4016.pdf

    So a couple questions crossed my mind.

    First question, asked three ways: How is zero defined? What does zero match in the real world? Is zero a reference for white in a print?

    Second: Why does the B&W curve lack the reference?

    Open to other thoughts here too.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  3. #3
    markbarendt's Avatar
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    Oh and am I right in my definition of Log H?
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  4. #4
    Bill Burk's Avatar
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    It's 10 to the power of 0 = 1. Given as lux-seconds.

    Log H is clearly explained on Page 6 of the workbook you linked... Yes it is "time-light" that you control when you change f/stop and shutter speed.

  5. #5
    Bill Burk's Avatar
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    I didn't answer the part about Log H Ref...

  6. #6
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    So we have "exposure" understood but:

    "We" are still confused on what "0" represents.

    "We" are still confused about why "0" is at the thick (variable) end of the negative.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  7. #7
    Bill Burk's Avatar
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    Zero is 10 to the power of 0, which is 1, a whole lux second. So -1 and -2 are like tenths and hundredths of a second. More like the exposure that would be used on film...

  8. #8
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    Hah, Bill, beat me to it while I was looking at the refs to refresh my memory. Good thing I refreshed the screen first.

    PE

  9. #9
    markbarendt's Avatar
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    Cool, I get it.

    So, in layman's terms, zero essentially defines a standard amount of illumination. A whole lux second.

    That explains the longer curve left of zero for Portra 400, vs 160, and the difference in offset from 0 to Log H.

    Thanks
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  10. #10
    Bill Burk's Avatar
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    Hey Mark,

    You're pretty much right...

    Just in case it hasn't sunk in yet. The scale of the x-axis is logarithmic. So it goes from left to right like 10 to the minus 3, 10 to the minus 2, 10 to the minus 1, 10 to the zero power, 10 to the first power. This works out as 0.001, 0.01, 0.1, 1, 10.

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