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  1. #41
    RalphLambrecht's Avatar
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    michael,please read ssteven's multiple and highly-educational postings concerningspeed points and systems to measure film speed. most of themworkwith a toe densityor shadow contrastto determine film speed.at the end of the day, you have to pick a method that works for you.snsel's assumption about zone Ihaving a target density of 0.1works very well in my opinion.what assumption do you work with?
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  2. #42

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    Ralph - I've participated in Stephen's threads - that's why I made the mouse trap comment. He challenges us to think critically about the "traditional" wisdom, rules, parameters, targets etc.

  3. #43
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    Quote Originally Posted by Michael R 1974 View Post
    I don't know where/if anyone called it a universal speed point. As you know it is simply a common targetted net negative density called "Zone I" in most Zone System books/methods, used to determine a working EI that presmubaly will lead to "full" local contrast around the "Zone III" density.
    But how legitimate is that? You are referring to a system/method and what it states. Does the theory support the premise and if so where is it? And the reason I used universal is that it is the speed point only in a specific situation and cannot be applied to all situations.

    One of the questions I propose is what is film speed. And one of the conclusions is that there is a difference between film speed and exposure. This is a distinction not frequently made.

  4. #44

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    Not disagreeing with you. I was simply describing a common approach to exposure index determination. The legitimacy of it is another story. Further, even if 0.1 above Fb+f is "correct", depending on how you test for the exposure that produces that density, you can get all sorts of exposure index values. My approach to film speed is somewhat different (as we've discussed before), although it may or may not intersect with 0.1 above Fb+f depending on the case.

    I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?

  5. #45
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Further, even if 0.1 above Fb+f is "correct", depending on how you test for the exposure that produces that density, you can get all sorts of exposure index values.
    Exactly my point. Stuff everyone needs to be aware of when considering testing.


    I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?
    Many systems, including Zone System, considers the fix density speed point of 0.10 the same as the minimum exposure / shadow exposure point of exposure. In fact, the just black printing method is predicated on this concept. Film speed is a standardization for comparison between films and a guide for exposure. According to the standard model and not factoring in personal exposure preference, shadow exposure isn't intended to fall on the speed point.
    Last edited by Stephen Benskin; 01-15-2013 at 01:03 PM. Click to view previous post history.

  6. #46

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    I see now. I think my approach is more consistent with the standard model, at least in the sense I am concerned with comparisons. Ultimately for me the speed point is a means to an end, not a target in and of itself, the end being maximized local contrast. If a film/processing combination delivered a perfectly straight line from Fb+f onward (ie there existed no "toe"), my speed point would be nothing more than 0.01 above Fb+f.

  7. #47
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Ultimately for me the speed point is a means to an end, not a target in and of itself, the end being maximized local contrast.
    Another important point of theory generally missing in most methodologies. Film speed is about the shadow gradient and not a point of density. That's why the ISO standard has the contrast parameters. How many methods incorporate this concept?

  8. #48
    markbarendt's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?
    Having a well defined speed point is important when exposure placement needs to have a very specific relationship to the films toe.

    For me its more about "am I on the straight line somewhere?".

    I'm not suggesting shooting wild or without thought where important detail might be lost, just that an exact correlation between placement of print tones and the placement of tones on the negative is not that important to most of my work. I'd even suggest that that is true for many, many people.
    Mark Barendt, Beaverton, OR

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

  9. #49
    RalphLambrecht's Avatar
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    true but this so,because a point of density is much essier to measure than a gradient(contrst).besides being effective any method also needs to be practical.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  10. #50

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    Quote Originally Posted by Stephen Benskin View Post
    Another important point of theory generally missing in most methodologies. Film speed is about the shadow gradient and not a point of density. That's why the ISO standard has the contrast parameters. How many methods incorporate this concept?
    Perhaps I'm accidentally inventing the ISO standard for myself, or at least confirming it, albeit probably with the safety factor.

    Film speed as a target net density versus a reference point is an interesting issue when it comes to flare as well. I'm always told flare increases film speed. Well, in a way yes, but if the toe is flattened by flare, I haven't gained anything. In fact I've effectively lost "speed" because local contrast has been flattened in the shadows.



 

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