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  1. #31
    Stephen Benskin's Avatar
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    This example shows HP5P 135 developed to a CI of 0.56 in Xtol. The graph on the left shows normal exposure with a resulting negative density range of 1.06. The graph on the right shows a three stop "over" exposure with a resulting negative density range of 1.02.

    Click image for larger version. 

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  2. #32
    PeterB's Avatar
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    Thank you again Bill and Michael. Thanks also to Thomas, David, Matt and Jnanian.
    My plan is to slightly reduce my dev time. I still think differently about the effect of development on the shoulder and will write more about that later.

    regards
    Peter

  3. #33
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    Quote Originally Posted by Stephen Benskin View Post
    This example shows HP5P 135 developed to a CI of 0.56 in Xtol. The graph on the left shows normal exposure with a resulting negative density range of 1.06. The graph on the right shows a three stop "over" exposure with a resulting negative density range of 1.02.
    Stephen, thanks for those curves. It shows that for a 3 stop overexposure , highlights (up to Zone VIII ?) will remain uncompressed. However in my process when I consider one more highlight zone than you do plus one more stop of over exposure, my theoretical max neg density will be 2.1 which is right at the limit of Ilford's curve and beyond that I assume it begins flattening out. There appears to be very little published data available for the shoulder sections of characteristic curves across all the development times. My next post will talk more about the shoulder sections.
    Last edited by PeterB; 05-28-2013 at 10:15 PM. Click to view previous post history.

  4. #34
    PeterB's Avatar
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    If possible I would like to make a very general statement about a film's shoulder (reached due to overexposure). Is it true that in general the following set of curves will represent the relationship in the shoulder area to increasing development times ? Note dev times might get too short to achieve Dmax as I show in the lowest curve.

    If my graph is not general enough, then what generalisation could we make about the way a curve's shoulder is affected by increasing dev times ?? (you must ensure sufficient over exposure is given to define all of the shoulder right out to Dmax)

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  5. #35
    markbarendt's Avatar
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    To your generalization. No.

    In general, as development is increased the curve gets steeper.

    It can be said that each emulsion/developer/technique combo creates a unique set of curves.

    It can be said that some films will shoulder off as you have shown, but its not a general truth. For example, TXP reaches 2.8ish with almost no bend and gets well over 3 with just a little, the shoulder is still really steep though.

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    DR5 claims a D-max of about 3.3 for HP-5 chromes.
    http://www.dr5.com/blackandwhiteslide/hp5dev-1.html

    So where do we start bumping D-max for a given film? Where do we start shouldering? I don't know.
    Last edited by markbarendt; 05-28-2013 at 11:46 PM. Click to view previous post history. Reason: Fix link and typo
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  6. #36
    PeterB's Avatar
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    OK Mark, so I had assumed that we keep every other variable fixed except development time. Surely we can say something about each successive shoulder for increasing dev times. How about "As we increase dev time, the shoulder of the curve will begin earlier and reach Dmax sooner".

    regards
    Peter

  7. #37
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    This example shows HP5P 135 developed to a CI of 0.56 in Xtol. The graph on the left shows normal exposure with a resulting negative density range of 1.06. The graph on the right shows a three stop "over" exposure with a resulting negative density range of 1.02.

    Click image for larger version. 

Name:	HP5P - Normal and 3 stops exposure.jpg 
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    Nice to see your program coming to the aid of a forum discussion!

    PeterB, The reason our curves end abruptly on the right, is that "we" try to catch the toe in our tests and haven't done studies of gross overexposure... All it would take to see how far out the straight line extends... would be to remove a ND filter from the well of the sensitometer, pop a test, and develop and measure it. I believe there is a great long straight line ahead.

  8. #38
    PeterB's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Nice to see your program coming to the aid of a forum discussion!

    PeterB, The reason our curves end abruptly on the right, is that "we" try to catch the toe in our tests and haven't done studies of gross overexposure... All it would take to see how far out the straight line extends... would be to remove a ND filter from the well of the sensitometer, pop a test, and develop and measure it. I believe there is a great long straight line ahead.
    Thanks Bill. I'm curious as to why films are rated with so much latitude for over exposure but virtually none for under exposure ?

    regards
    Peter

  9. #39
    markbarendt's Avatar
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    The curves for TXP aren't showing it reaching D-max so, no to that part at least.

    TMY can hold about 14 stops on the straight line IIRC, so if you had used TMY instead of HP5 for the shots that started this thread you could have exposed another three stops (7 stops up total) before you even got to the shoulder let alone finding D-max. So again no, the generalization doesn't work.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  10. #40
    markbarendt's Avatar
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    Quote Originally Posted by PeterB View Post
    Thanks Bill. I'm curious as to why films are rated with so much latitude for over exposure but virtually none for under exposure ?

    regards
    Peter
    Shutter speed is my bet.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

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