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  1. #51
    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, Ignacio, CO

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

  2. #52
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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

  3. #53

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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.

  4. #54
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    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.
    Like with film speed calculation, what is considered the minimum useful gradient, while determined using a flare free test, has been adjusted to reflect the affects of flare.

    In my opinion most of the testing methods are more about producing a range of EIs that reflects the author's personal taste, whether it's about having enough of a safety factor, or producing enough shadow contrast, or producing a negative that works in conjunction of the just black printing test. For all but specialty developers, speed testing isn't really all that necessary and with specialty developers a simple comparison is between the two developers is all that is really required. It's more important to personalize the way the photographer likes to expose (personal EI) and that can be determined using the ISO speed as a foundation.

    I believe one of the reasons why there's such a fixation on speed determination is that with simplified Zone System method of sensitometric testing, you don't produce a curve, but only two points of density. In order to determine the contrast, you first need to find the base point. This is backwards from general sensitometric testing. There the film is exposed and developed to differing degrees. The contrast is then determined along with the effective film speed for that contrast. Has the simplification involved in such methods as the Zone System unintentionally overemphasized the importance of speed and a speed point and under emphasized of the importance of contrast determination? There seem to be far more discussions on speed and how to test for it then there are about contrast.

  5. #55
    markbarendt's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    There seem to be far more discussions on speed and how to test for it then there are about contrast.
    And when contrast is talked about it seems tied to speed point rather than SBR or preferred print contrast.
    Mark Barendt, Ignacio, CO

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

  6. #56
    Bill Burk's Avatar
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    From a recent family of tests I contact printed a negative image of a step wedge which fit the whole 21 steps on paper. (An original step wedge wouldn't do this - but a negative step wedge developed Normal would).

    I cut chips from the contact print to make a Zone System sticker for my Weston Master II meter last night.

    I wanted to include one stop of flare in my Zone System sticker, so I picked the next step above blackest black for my Zone 0 chip.

  7. #57

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    Quote Originally Posted by Stephen Benskin View Post
    Has the simplification involved in such methods as the Zone System unintentionally overemphasized the importance of speed and a speed point and under emphasized of the importance of contrast determination? There seem to be far more discussions on speed and how to test for it then there are about contrast.
    Well, the first thing I'd recommend to anybody using any kind of Zone System testing methodology is to produce a full curve, not just target a Zone I and Zone VIII density. To me, everything is about contrast - ie the shape of the entire curve since I am ultimately concerned with printing.

    As I've said, the speed point is a means to an end. I'm concerned with local contrast.

    But even when contrast is considered in Zone System testing, there should be a lot more discussion about local contrast (ie not just CI or Gamma) and the paper curve. After all, how many people come away from Zone System contraction methods (including extreme contractions) thinking N-4 necessarily means Zone XII will print with good detail because it has a Zone VIII density in the negative?

    But I'm getting ahead of the discussion there. We've sort of disagreed regarding the practical use of measures like CI in the past - mostly because I am typically dealing with significantly wider subject brightness ranges than average.

  8. #58
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    As I've said, the speed point is a means to an end. I'm concerned with local contrast.
    It is a means to an end, but that doesn't mean it's arbitrary. If done according to the ISO Standard, the speed point can yield useful information. It defines the relationship between the meter exposure and the shadow exposure, it defines the local contrast as well as determining the point of useful minimum exposure (0.29 log-H units to the left where the gradient is 0.3x the average gradient).

    This is what I mean about questioning the steps in any methodology. Most methods are just variations of the basic Zone System approach where the speed point is unconnected with the three elements list above. While the 0.10 density may have come from the ISO speed standard (the ZS use of 0.10 probably was derived from DIN or the early British standard), it has been misinterpreted or simply impoperly applied.

    Using the ISO speed standard we know the speed point is 1.0 log-H units to the left of the metered exposure point. According to many popular methods, the speed point is four stops down or 1.20 log-H units below the metered exposure point. Obviously the two methods will produce film speeds typically differing by two-thirds of a stop. This is why Zone System testing consistently produces EIs 1/2 to 1 stop slower than the ISO speed. While the 1.20 log-H method will produce quality negatives and will create perfectly acceptable EIs, it shouldn't be regarded as a reliable way to determine film speed. Of course, if the additional exposure from the lower EI matches your style, why not save the time and just use the ISO speed and make the 2/3 stop adjustment. Afterall, what's the point of doing the test if it's not going to produce a reliable number.

    Most of the authors won't explain this difference (mostly because they aren't aware of it), so when shopping around for a non-ISO testing method, understanding the theory is important. Just because someone wrote it down doesn't mean it's true. This doesn't mean you shouldn't use a non-ISO method. I'm just suggesting to use it knowingly.

  9. #59
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    To tell the truth I am bit lost here.
    Reading all this.
    All I can say is that I use the 0.1 speed point as my first reference. I plot my curves to see how the shape is. This is important for me. When I use my adopted method (a bit of this a bit of that) I can usually make my print at about Grade 2 (to simplify this using Grades), I increase the development times slightly because I like to use unsharp masks and the funny thing is I land at a contrast of about 0.62 which is what most published time use as a standard. However my actuall development times are always less than published and I always have to overexpose.
    I am always amazed and wondering when people say they use box speed. It doesn't make sense to me.

  10. #60
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    Quote Originally Posted by Stephen Benskin View Post
    This is why Zone System testing consistently produces EIs 1/2 to 1 stop slower than the ISO speed. While the 1.20 log-H method will produce quality negatives and will create perfectly acceptable EIs, it shouldn't be regarded as a reliable way to determine film speed. Of course, if the additional exposure from the lower EI matches your style, why not save the time and just use the ISO speed and make the 2/3 stop adjustment. Afterall, what's the point of doing the test if it's not going to produce a reliable number.
    So the bottom line of the endless Zonistas testing [This is not an attack on Stephen, I am just using his data to make a point] is a difference of less than a stop based on poor assumptions and uncalibrated equipment, sloppy testing and developing that the Zonistas are basing their work on. << Duh>> with the present dynamic range of both black & white and color C41 film of 12 to 14 f/stops depending on the choice of film, developer, developer dilution, and whom you choose to believe, less than one stop change will not produce any signifacant advantage or disadvantage. That being the case, why was time, money, film and chemicals to do all this testing when one will end up with essentally the same results using the box speed? Testing was useful when cameras and light meters were not that accurate, the results from the variation developers' result was wider ranging for all the dilution recommendation at that time1 and the film quality and dynamic sensitivity range was narrower.






    1Since then Kodak and others recommend a narrower range of dilution, staying closer to 1:1 and 2:1 than the 4:1 then.
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