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  1. #11
    AndreasT's Avatar
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    Michael I enjoy these threats and post of you Stephen and Bill including a few others. I have learnt a lot more, get confused very often. This certainly helps to understand all this better.
    Exposure is the most important single factor in photography in my opionion and it is discussed too little.

  2. #12
    AndreasT's Avatar
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    Am I correct or incorrect in say that the Delta-X criterion is more similar to th CI from Kodak. Looking at curves near the foot it seems to make sense regarding film speed. Now am I over ambitious in saying when I get my EI there is no need to change the EI when pushing or pulling?

  3. #13
    Stephen Benskin's Avatar
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    Quote Originally Posted by AndreasT View Post
    Am I correct or incorrect in say that the Delta-X criterion is more similar to th CI from Kodak. Looking at curves near the foot it seems to make sense regarding film speed. Now am I over ambitious in saying when I get my EI there is no need to change the EI when pushing or pulling?
    The lower gradient part of CI uses the same basic theory as the fractional gradient method. Long toed films are where the influence is greatest.

    Film speeds don't change much with fraction gradient / Delta-X. The pre 1960 standard didn't have an aim contrast for film development (it did have a minimum). While the Delta-X Criterion uses a fixed density point, the Delta-X point moves in relation to the fixed point as the average contrast changes. This tends to compensate for the shifting of the fixed density point.
    Last edited by Stephen Benskin; 02-28-2013 at 01:37 PM. Click to view previous post history.

  4. #14
    Rafal Lukawiecki's Avatar
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    I am excited to see the beginning of a (I hope) another illuminating chapter in the saga of the variables of the tone reproduction cycle and their relationships. Count me in to lurk over you. Stephen, Bill, Michael, and others—thank you.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  5. #15
    Stephen Benskin's Avatar
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    Here's a comparison of speeds derived from the fixed density method and the Delta-X Criterion.

    Click image for larger version. 

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    Except this is not as much a comparison between two methods as it is between an accurate method, Delta-X, and the erroneous and inaccurate use of another.

    This is why the Delta-X speeds change little with changes in development.

    Click image for larger version. 

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    As the gradient changes with development and the fixed density point shifts left and right, the fractional gradient point's relationship to the fixed density point changes but it's log-H remains relatively constant.
    Last edited by Stephen Benskin; 02-28-2013 at 11:52 PM. Click to view previous post history.

  6. #16
    ic-racer's Avatar
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    Whoa, you can't start a thread about fractional gradient approximations without discussing "W speed"...
    Attached Files
    Last edited by ic-racer; 03-01-2013 at 08:54 AM. Click to view previous post history.

  7. #17
    Stephen Benskin's Avatar
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    Quote Originally Posted by ic-racer View Post
    Whoa, you can't start a thread about fractional gradient approximations without discussing "W speed"...
    Delta-X was adopted for the ISO standard. W speed is more of a historic footnote for being the runner up. As the paper says, W speed "is of particular interest in the mathematical theory of the shape of the sensitometric curve and its relation to speed." It's worth knowing for that, but it has never been used as a film speed method. Seriously, film speed can be a confusing topic and W speed will only add to the confusion unnecessarily.
    Last edited by Stephen Benskin; 03-01-2013 at 02:30 PM. Click to view previous post history.

  8. #18
    Bill Burk's Avatar
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    My take-away from the W speed article that these different speed ratings are compared based on how well they correlate to the "Picture Tests".

    Then the writer makes an outlandish statement that I will challenge: "It is, of course, too time-consuming to use the print-judgment method."

    "Of course"? "Too time-consuming"?

    Look at how much time we spend talking about film speed testing.

    It might be fair to say that is more time-consuming than making some prints and showing them to your friends.

    I'm not suggesting to throw out the tests... Just providing some necessary perspective.

    I still like to test to ASA triangle and 0.1 density. Then I accept Delta-X Criterion as justification that I can use whatever speed I discover when I get as close as I can to ASA parameters... And I use that speed for all my varied development times (N-1, N and N+1 etc.), because it is easier to pick one speed than use a sliding EI... and because it is probably correct.

  9. #19
    Stephen Benskin's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Then the writer makes an outlandish statement that I will challenge: "It is, of course, too time-consuming to use the print-judgment method."

    "Of course"? "Too time-consuming"?

    Look at how much time we spend talking about film speed testing.

    It might be fair to say that is more time-consuming than making some prints and showing them to your friends.
    The ring-around test can probably be thought of as a very stripped down personalized version of the first excellent print test.

    I have to agree with Nelson. It took 18 months to produce the negatives for the first excellent print test.
    Last edited by Stephen Benskin; 03-02-2013 at 01:08 AM. Click to view previous post history.

  10. #20
    Bill Burk's Avatar
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    I would have enjoyed watching Nelson and Jones at work.

    I meant to emphasize that my take-away was...

    The ultimate speed criterion is the Picture Tests themselves.

    Anything else is an attempt to correlate to the Picture Tests.

    As you like to say, Stephen, hiding in plain sight.

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