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  1. #71
    PeterB's Avatar
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    thanks Rafal. Feel free to pm them to me. I'll check them out in about 18-24 hours.

  2. #72
    PeterB's Avatar
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    Thanks Rafal, I tried again and managed to see the curves. I note you don't have any data in the film speed curve for higher than N+1. I initially thought it was because you only developed for 16 minutes but I see if you added another point out at N+2 on the summary plots that you would have hardly any difference in film speed between N+1 and N+2. This is a consequence of your diml speed curve asymptoting. Additionally your film speed curve is concave up whereas mine is concave down for nearly the same combination of film and dev (I used XTOL 1+2 rather than 1+1).

  3. #73
    Rafal Lukawiecki's Avatar
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    Thanks, Peter. I was also a little surprised by the concave up, when I saw it, and I have no real explanation why this happened. I was wondering if, perhaps, some lack of evenness in illumination could be the reason for it, but a test sheet, exposed with ND, is pretty even.
    Rafal Lukawiecki
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  4. #74
    CPorter's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    I guess what I don't understand about things like CI is, why "summarize" the curve with a straight line of best fit when you already have the full curve?? Why not simply plot the curves and compare them?
    In parusing this thread, I found this to be a striking observation...............this is precisely the sentiment made clear in The Negative.....points along a curve connected by a straight line are not touted in the The Negative as having any significance toward any ZS analysis of characteristic curves. It's the comparison of two curves in their entirety that provides the best evaluation of a film in a developer, so says the author. Gamma, which applies to "true" straightnline portions of any curve, is given more merit than points connected by a straightline. Whether this is agreed with or not is kind of beside the point, it's just an observation. I don't bother with CI myself, I just compare the curves, I find that to be most illuminating and the most straight forward.

  5. #75
    Stephen Benskin's Avatar
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    Could somebody post the curves?

  6. #76
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Could somebody post the curves?
    Stephen, in post #68 of this thread I attached the full spreadsheet with the data points and the curves for both HP5+ and 320TXP. If the file does not open for you, however, I would be happy to extract the curves, please let me know.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  7. #77
    Rafal Lukawiecki's Avatar
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    Quote Originally Posted by CPorter View Post
    I don't bother with CI myself, I just compare the curves, I find that to be most illuminating and the most straight forward.
    I don't have your experience of reading the curves, as I have only started sensitometric analysis of my materials. I have no doubt, however, that you are right. Re-reading BTZS, plus many good points raised on this, and on other related threads, have opened my eyes to the holistic nature of the tone reproduction cycle. It is clear to me that subtleties of the cycle cannot be summarised by just a single gradient number.

    Nonetheless, I found it necessary to figure out developing times for my N, N-1, and N+1 negatives. I found that knowing an aim DR, as described by BTZS, or a gradient, G-bar, or CI, all are perhaps crude, but practical ways to summarise the requirements of the printing process for the film development output. This was my main goal of this calibration exercise.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  8. #78
    Stephen Benskin's Avatar
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    Quote Originally Posted by Rafal Lukawiecki View Post
    Stephen, in post #68 of this thread I attached the full spreadsheet with the data points and the curves for both HP5+ and 320TXP. If the file does not open for you, however, I would be happy to extract the curves, please let me know.
    Rafal, I'm not able to plot/find the curves, so if you can extract the curves, I would appreciate it.

  9. #79
    Stephen Benskin's Avatar
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    Quote Originally Posted by Rafal Lukawiecki View Post
    It is clear to me that subtleties of the cycle cannot be summarized by just a single gradient number.
    And it was never meant to be. Just like the average driving speed in a trip doesn't specify the time spent at stop lights. It's an average. The average gradient, which includes the testing conditions, offers a general picture of the the way the film responds to exposure and development.

    For any film curve, the average gradient for a 1.30 log-H range might be different for the average gradient if measured using a 2.20 log-H range. How it's measured is part of the answer. Think of the arguments for and against the various methods such as Gamma, Ilford's Average gradient, and Kodak's Contrast Index. And while we're at it, how much information about the film curve does a simple density range offer as some methods suggest using?

    Once again, nothing's perfect especially when you are attempting to quantify a subjective response. And as with the NDR / LER relationship, what better course is there to follow.
    Last edited by Stephen Benskin; 10-14-2012 at 09:19 PM. Click to view previous post history.

  10. #80
    Bill Burk's Avatar
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    Hi Rafal,

    Haven't had time to plot your curves manually, but here's the graph paper I would use. The green lines correspond to your step tablet actual densities... I find graphing goes faster when I have green lines for each x-axis step...

    http://www.beefalobill.com/images/sensitometry-RL1.pdf

    The top "film speed" scale is not calibrated to your setup. Cut it off and slide it left or right to get an idea of your relative film speeds.

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