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  1. #131
    Stephen Benskin's Avatar
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    Quote Originally Posted by markbarendt View Post
    Chuck are you carrying through specific subjects/zones measured in the scene or are your zones defined at the negative?

    What I'm getting at is that if measured at the negative then camera/scene based flare wouldn't be represented, right?

    Look alone the bottom of the x-axis. The log-H range is 2.10 (7 stops). That's approximately the normal scene luminance range, not the in camera illuminance range at the film plane (exposure range). The important point is that the combination of the NDR and the log-H range still equates to a normal contrast negative, but that the 1.20 or traditional ZS 1.25 is a projection or construct in order to compensate for interpreting real world conditions on something produced in non real world conditions. This method can be used instead of adding a separate camera image curve or adjusting the log-H range of measurement to reflect the exposure range.

    Phil Davis discusses this concept, in brief, in BTZS 3rd ed, Analyzing Film Curves, p 95.

    The question has never been about quality in the final results. The discussion has always been about understanding what's going on in the process.

    Have you ever seen a film curve that shows the effects of flare like below?

    Click image for larger version. 

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    This is a similar concept to ZS contrast determination in that it too is a construct. It shows how flare effectively changes the film density. Putting it all on one graph eliminates the need for a camera image curve, but it doesn't illustrate how flare acts upon the film curve in reality. For that, a two quadrant curve is required.
    Last edited by Stephen Benskin; 02-20-2012 at 08:35 AM. Click to view previous post history.

  2. #132
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    Quote Originally Posted by markbarendt View Post
    Chuck are you carrying through specific subjects/zones measured in the scene or are your zones defined at the negative?

    What I'm getting at is that if measured at the negative then camera/scene based flare wouldn't be represented, right?
    Mark, I have to admit I'm not quite sure what you are asking me here. The curve is created by an in-camera exposure of a Stouffer 21-step tablet, the densities read and plotted. Perhaps my mind is foggy this morning, sorry. Perhaps rephrase the question.

  3. #133
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    Chuck I think you answered the question, but here's a rephrased version.

    The zones you are using are defined by the step wedge in the scene, correct?
    Mark Barendt, Beaverton, OR

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

  4. #134

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    Stephen, sorry for not being more active on this of late. Going back to my previous post, I guess all I'm saying is thanks to these threads, I have a better understanding of how flare can alter the low end of the H&D curve once we are "in the field". It has caused me to change the nomenclature on my curve graphs - where I used to have equally spaced zone numbers on the x axis, I now label those spacings as metered exposure values.

    But I suppose beyond understanding what flare is and how it impacts things, I admit I do get somewhat lost when it gets more quantitative, not that this has really caused any problems in my exposure/development/printing. However I am still unclear on things like - what constitutes a high flare vs low flare situation?

    As I said, the "in the lab" part of my film/development tests for EI, plus/minus development etc are fairly basic, but somewhat tailored to the conditions I'm often working under in the field:

    1. I use a brightly lit white card and expose in camera to determine EI (admitedly this probably ends up understating EI, and that is borne out when I go to the "outside the lab" tests).

    2. I plot a curve from threshold up to zone XV, the reason being I'm often dealing with very long SBRs in my work. This is why I feel it is important to know the shape of the curve, all the way up to zones XIV-XV under different development scenarios - not understanding that part of the curve and how variable it is, is where many people go wrong with severe contractions, stand development etc.

    When I do these white card tests I meter with the same 1deg spot meter I use in the field, keeping as close to the lens axis as possible. I don't know if there is any flare in the metering, or the camera exposures. Based on previous responses from you and Bill Burk to similar questions, I assume flare to be minimal in my tests.

    To me the last graph you posted (post #131) is really what it all comes down to when we talk about flare. This is really the kind of "flare overlay" we all need when we plot curves. The question is, how? It is too variable. What do we assume for an average case - this gets back to my question about how to tell when surveying a scene whether it is high or low flare? And how is that flare impacted by the choice of lens, luminance placements, exposure time etc?

  5. #135
    Stephen Benskin's Avatar
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    Quote Originally Posted by CPorter View Post
    But, a ZS practitioner (if he or she considers themselves strict about it) does not really consider CI or any other measurement of contrast that connects points on the curve with a straight line. It's the comparison of the entire curves of at least two films or one film with different developers that is considered most valuable.
    Chuck, I was confused at first by this response until I realized it was paraphrased from The Negative. Let me post the whole section on Gamma and contrast from page 88. Iíve bolded the part that concerns Adamís opinions.

    ďGamma and Contrast

    The filmís contrast can be measured by determining the slope of the straight-line portion of the curve. The slope is the ratio of the density change to the exposure change in the straight-line region, and is given the name gamma. Gamma, then, equals change in density divided by change in log E in the straight-line region. A film with a higher value for gamma will have more contrast than a film with lower gamma; it should be clear, for example, that a one-zone exposure change produces a greater density interval with a higher gamma film than with a lower gamma film.


    There are some limits to the usefulness of gamma as a measure of negative contrast, however. For one thing, not all films have a long region that closely approximates a straight line. Even when a true straight-line region is present, gamma gives no measure of the nature or extent of the toe region of the film, which is of great importance in photography. Several different contrast measures have been developed over the years with the intention of supplanting gamma as a contrast indicator. One such index is called mean gradient (written G), and another is the Contrast Index (CI) system used by Eastman Kodak. Both approaches define limits on the film curve to be connected by a straight line, and the slope of this line is then measured. I find such systems confusing and uncertain in applied photography, and I still consider gamma the most useful figure. No index, including gamma, is nearly as informative as comparing the entire curves of two films, or of one film under different processing conditions. In addition, many contemporary films have exceptionally long straight-line sections which, in my opinion, definitely change the concepts of contrast measurement.Ē

    First I have to admit itís hard to make a proper evaluation when you only spend two paragraphs on a subject that could fill chapters, butÖ

    Adamís is misrepresenting the purpose of the gradient methods when he attempts to associate the determination of contrast with comparing film characteristics. The different versions of the average gradient methods are no more about comparing the characteristics of film curves than is the Zone System's method for contrast determination. I believe this is just an attempt to quickly rationalize away concepts he doesn't want to deal with nor understands well enough to properly evaluate. I'm sure he also didn't want put in too much effort making a case for a method other than his own. Itís hard to sell books if you canít make people believe they should use your methodology.

    I believe I am correct in concluding he didnít have a firm grasp on the different forms of contrast determination because 1). he admitted that he found the systems confusing, and 2). he considers Gamma to be the most useful "figure" even though the original unmodified version of Gamma had already been thoroughly challenged by that time.

    Personally, I donít think thereís enough included in those two paragraphs to make any conclusions on the viability of any methodology.
    Last edited by Stephen Benskin; 02-20-2012 at 09:54 PM. Click to view previous post history.

  6. #136
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    Quote Originally Posted by Stephen Benskin View Post
    Personally, I donít think thereís enough included in those two paragraphs to make any conclusions on the viability of any methodology.
    You may be right, but I don't care; it's not important to me.

    Once again, I never emphasized a lack of viability of using CI, not once, only that it's not useful to me in my use of the ZS (after all that's the way I learned it), despite the misgivings you have about it. CI values themselves have no bearing on any decision I make, that has been my only sentiment. I've no good reason to start considering it the way you and Bill do given the personal success I'm having after never really thinking about it at all. Call that mindset what you will, it's irelevant. I see that it is enormously important in the way that you and Bill and I guess others operate, but not for me in the way I operate----you seem to have a hard time accepting that. I regret ever mentioning it all.

  7. #137
    Stephen Benskin's Avatar
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    Michael, I'll try to touch on some of these questions.

    Quote Originally Posted by Michael R 1974 View Post
    When I do these white card tests I meter with the same 1deg spot meter I use in the field, keeping as close to the lens axis as possible. I don't know if there is any flare in the metering, or the camera exposures. Based on previous responses from you and Bill Burk to similar questions, I assume flare to be minimal in my tests.
    Yes, I would considered it virtually flare free.

    I use a brightly lit white card and expose in camera to determine EI (admitedly this probably ends up understating EI, and that is borne out when I go to the "outside the lab" tests).
    It's not as much about the white card as it is about interpreting the results from a flare free test. Remember the thread about the relationship between the speed point and the metered exposure point? The reason why the ISO speed point is only 1.0 logs from the metered exposure point while the scene luminance range between the metered exposure and the shadows is 1.3 log is because you are projecting the effective shooting conditions onto a no flare test. Flare reduces the range from 1.3 to 1.0 or to put it another way, flare increases the film speed from where it would be without it. The higher the flare factor, the faster the effective film speed.

    2. I plot a curve from threshold up to zone XV, the reason being I'm often dealing with very long SBRs in my work. This is why I feel it is important to know the shape of the curve, all the way up to zones XIV-XV under different development scenarios - not understanding that part of the curve and how variable it is, is where many people go wrong with severe contractions, stand development etc.

    However I am still unclear on things like - what constitutes a high flare vs low flare situation?
    It's more likely from your experience, you know more about flare in extreme situation than almost anyone else. Many of the more normal conditions likely to be experienced tend to fall into predictable rules and categories of scene types and lighting conditions. Most of which I am rusty on. There are a few papers by Loyd Jones that cover much of this in detail. All three of them were published in The Journal of the Optical Society of America. They are listed chronologically and they are:

    The Brightness Scale of Exterior Scenes and the Computation of Correct Photographic Exposure.
    Sunlight and Skylight as Determinants of Photographic Exposure. I. Luminous Density as Determined by Solar Altitude and Atmospheric Conditions.
    Sunlight and Skylight as Determinants of Photographic Exposure. II. Scene Structure, Directional Index, Photographic Efficiency of Daylight, Safety Factors, and Evaluation of Camera Exposure.

    The first and third paper deal more directly about what you are interested in. They are a tough read. I probably should review them too. If I run across anything I think will be helpful, I'll post it.

    On the average, the shorter the luminance range the lower the flare factor and vice versa. Flare tends to act like a buffer with the degree of processing. You don't have to reduce development as much with scenes with a large luminance range and you don't have to extend the processing as much with scenes with shorter luminance ranges than would be indicated without factoring in flare. Then there's the whole perception of the finished image. If the shot is toward the sun, the viewer will expect for the shadowed areas to be hazy. I believe the third Jones paper covers much of this.

    Michael, This is a really big subject. Maybe if the questions are a little bit more specific or something, I could be more specific with my answers.

    To me the last graph you posted (post #131) is really what it all comes down to when we talk about flare. This is really the kind of "flare overlay" we all need when we plot curves. The question is, how? It is too variable.
    That graph isn't really how flare works on the film curve, below is how it really works.

    Click image for larger version. 

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    Now, you don't need a camera image / flare curve to make it work. Simply use the exposure range from combination of the scene's luminance range and flare and apply it to the film curve. It sounds like you are already doing this.

    Is flare too variable to have to do this? Yes and no. Yes, no matter what it's always going to be a guesstimate. No in that phenomenon tends to have statistical averages and follow a bell curve, so you have a better chance to be within your target range if you factor some of it in.

    Odds are you are already factoring it in depending on how you measure the film. This is something I've discussed ad infinitum. The manufacturer's published processing times have flare factored in too. So most people incorporate flare into their film processing whether they know it or not. And if you are already incorporating a stop of flare into your process, and if the flare factor is plus or minus another stop or so, this difference can easily be off-set by a variety of factors like scene luminance range, the nature of the subject, how the tones are distributed, choice of paper grade, and personal taste.

    Didn't I recently say something about why Kodak might use a fix flare model for their contrast determination instead of the more realistic variable flare model? The question comes down to how accurate does a model have to be. Understanding theory is not only about attempting to achieve a level of control over the process. It's about understanding the process in order to know the degree of what can and cannot be controlled.

    And how is that flare impacted by the choice of lens, luminance placements, exposure time etc?
    Another question that could be the topic for a whole new thread. Off the top of my head - Lens? Angle of view, coated or uncoated, size of image circle, number of elements, etc. Distribution and size of scene luminance? Absolutely, much of first and third Jones paper is on that topic. Exposure time? I'm not sure but it doesn't seem like it should. I'll have to keep an eye out for that one.

    Sorry if this post comes off as disjointed and rambling.
    Last edited by Stephen Benskin; 02-21-2012 at 03:43 AM. Click to view previous post history.

  8. #138
    Bill Burk's Avatar
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    Chuck,

    Your curves showing HC110 and D-76 clearly show how meaningful it is to compare curves in their entirety.

    But the corollary was not true, the line between two points does matter in classic ZS, so I had to say something.

    You already got my drift and responded and I'm good with that.

    I'm not going to tell you to change your NDR, though I continue to explore the interesting fact that you chose 1.2 and I chose 1.0

    For the amusement of all, Minor White aimed for NDR 1.5

  9. #139

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    Quote Originally Posted by Stephen Benskin View Post
    On the average, the shorter the luminance range the lower the flare factor and vice versa. Flare tends to act like a buffer with the degree of processing. You don't have to reduce development as much with scenes with a large luminance range and you don't have to extend the processing as much with scenes with shorter luminance ranges than would be indicated without factoring in flare.
    This is what I have found in practice, and it is an overlay to my initial flare free tests. Typically when I'm photographing a predominantly dark scene with an intense light source in-frame, if I go strictly by my white card tests, I end up with higher shadow densities than I expect. When I first started doing zone system testing, I could not understand why every time I printed a negative, I almost consistently concluded I could have given the film a little less exposure (and therefore also given a little more development). Sometimes it is significant too, up to a stop or even more - as you've mentioned in previous threads. It is interesting to note what ends up happening in much of my work (low overall light levels but intense light sources in-frame) runs counter to what one might expect using a straight zone system approach. The lower the overall light level and higher the total contrast, the higher my working EI!

    Thanks for replying to my admittedly non-specific post. It helps answer some of my general questions about what makes for high vs low flare.

    Here is a follow up question though: In Adams and other sources, generally studio work is referred to as an example of low-flare conditions. I am not sure why that would be, other than the fact all the luminances in the scene are controlled to eliminate extremes. But what confuses me more, is the frequent assertion (again in Adams, but in other books too) that a film with a relatively "long toe" is generally more useful under low flare conditions such as those encoutered in studio work. Why would this be? To me it seems the opposite.

  10. #140
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    Quote Originally Posted by Bill Burk View Post
    Chuck,

    Your curves showing HC110 and D-76 clearly show how meaningful it is to compare curves in their entirety.

    But the corollary was not true, the line between two points does matter in classic ZS, so I had to say something.

    You already got my drift and responded and I'm good with that.

    I'm not going to tell you to change your NDR, though I continue to explore the interesting fact that you chose 1.2 and I chose 1.0

    For the amusement of all, Minor White aimed for NDR 1.5
    Bill, I tried to paraphrase my statement regarding gradient as viewed in The Negative that Stephen previously highlighted, didn't do a good job I guess. I can't determine that the line connecting points on the curve to determine gradient matters in the classic approach to the ZS, but would be inerested in your point.

    When I learned the ZS, I chose 1.2 because that was indicated by AA in the text, for no other reason than that. It's working so well, I've not a good reason to deviate from it. I understand more today about gradient and CI, because of these threads, but not enough to cause me to change it.



 

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