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  1. #61
    smieglitz's Avatar
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    Quote Originally Posted by Ornello Pederzoli II
    You're right
    Sufficient.

    Quote Originally Posted by Ornello Pederzoli II
    that measured CI requires both (calibrated) exposure and development. But once the development conditions have been identified, that can serve as a reference. In this extended sense, then, CI can mean 'amount of development' without reference to exposure.

    In other words, if developing a TMX control strip in D-76 1:1 for 10 minutes at 68F produces a measured CI of 0.56 (using your tank and agitation method) then for all practical purposes all other TMX developed in the same way will be developed to/for (I'm not sure there is a distinction)
    I'm sure. There is a distinction.

    Quote Originally Posted by Ornello Pederzoli II
    a CI of 0.56, within the normal tolerances of development. It has become a reference at that point. You don't need to measure every time, unless you suspect some problem with the products or water. Labs run control strips regularly so they know how their film is being developed. Without a control strip, it is almost impossible to measure CI. Fortunately, you really don't need to. If normal scenes look right on normal paper (grade 2-3), you're doing fine.
    Yes. I understand all this.

    And thank you for this productive reply. Others trying to grasp the utility of CI may find it helpful.

    Joe

  2. #62
    Stephen Benskin's Avatar
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    Sandy, my point about SBR is that anyone can nit-pick someone else. Maybe I should have just said stop attacking OP, but I wanted to make a point. Sorry you missed it.

    I haven't look through Phil's book for sometime now. BTZS is a simplified version of sensitometry with some short cut tricks. I generally like to stick to the fundamental and scientistic concepts of sensitometry and tone reproduction and use the proper internationally accepted terms. I know there is more to sensitometry than BTZS just like you know there is more to film than just the Zone System. I've read the standards as well as the seminal papers on the subject. I'm able to explain K and the calibration of the exposure meter fairly well. I know the contrast parameter in the ISO film speed standard are not simply arbitrary values, but a way of converting the less than satisfactory fixed density method into the more accurate fractional gradient method. So, Sandy don't attempt to blow me off as someone who doesn't understand. I understand a lot better than you think especially if you are only able to use Davis as a source. If you want to talk theory, you've come to the right person. BTW, the attachment came from a program that I wrote.

    Oh, and if you're curious to know where there is proof that Davis' use of an arc with Ilford's average gradient is incorrect, I found it in paper from The British Journal of Photography, May 12, 1967 titled Contrast Measurement of Black and White Negative Materials. There is no author credited.

    Joe, I did say OP's example wasn't the best, but consider for a minute how it is possible to be correct in theory. If you have a scene with the statistical average luminance range of 2.20 and the statistical flare of 0.34 and develop the film to a CI 0.56, then the negative density range will be 1.05. What about the clear edges of the film. Didn't the edge also get developed to a CI 0.56? What about shooting a gray card? According to Sandy, a scene without a contrast range can't have a slope so it can't be developed to a given CI. Can a gray card be developed to a given CI? Of course. Can you determine CI with blank film of a single shot of a gray card? No, of course not. Is the blank film example a silly, bad example? Yes, but it also makes sense if you look at it a certain way. It's a thought experiment.

    The original poster was looking for a book to help him with Contrast Index. In the last post, I listed THE paper on it. There is also Photographic Materials and Processes, The Manual of Photography, Photographic Sensitometry, the Study of Tone Reproduction, and the section on Contrast Index in The Focal Encyclopedia of Photography.

  3. #63
    Stephen Benskin's Avatar
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    Quote Originally Posted by sanking
    How did you make the determination that the Kodak numbers are higher for both DR and SBR? When I compared the calculations with real plots for the two methods the DR and SBR were identical. The only practical difference between the two is that the Ilford G-Bar methos suggests a slightly higher EFS than Kodak's CI. This might, depending on the paper curve of the process, result in some differnce in the printing characteristics of the negative. But for all practical purposes the difference between G-Bar and CI is irrevelant.

    BTW, my reference is the 3rd edition of Beyond the Zone System and on page 29 Davis explains how Average Gradient, or G-Bar and CI (Contrast Index) are determined. It is same as one finds in Kodak and Ilford literature.

    Sandy King

    Not only is all of this wrong, the part on Ilford’s average gradient method suggesting a higher EFS approaches gibberish. These are methods to determine contrast – not speed. Joe’s post that Sandy is referring to has much more truth to it, but he doesn’t go far enough.

    Any information derived from testing is only accurate for the specific points tested. Every other point is just speculation. All the forms of contrast determination work in this way including the Zone System. You assume the curve between the lower and upper tested points is somewhat linear. Fortunately, most films are relatively linear, but the curve can be doing somersaults between these two points and still produce identical contrast indications. It can also have different characteristics outside the area tested. This shouldn’t matter except if that area of the curve will be utilized in practice. If the portion measured isn’t significantly long enough, it won’t take into account the section of the curve representing the highlights. If the portion measured is too long, it will utilize a part of the curve excluded in actual use, and depending on the curve shape may skew the results. So, it is critical to determine which portions of the curve measured are represented in actual use.

    The shape of the curve also plays an important roll. Linear curves will produce satisfactory results no matter the length of the portion measure. Long toed curves, on the other hand, will produce a lower contrast indication with a short measurement and a higher contrast indication with a long measurement. Curves that “shoulder off” produce the opposite results. This is where Joe fell short in his observation. He only covered one side. So, the two different methods of determining contrast don’t tend to produce any trend in results. They will produce different results depending on the shape of the film curve.

    As for Sandy’s conclusion that there is no distinction between the two methods…well, that has just been shown to be wrong. In a recent statement by Joe, he said "several of us have tried to be helpful and genuinely assist the thread originator with his question." How does Sandy offering bad information as fact and not opinion do that?

    And Joe, I wasn't trying to bait anyone. I simply don't believe ganging up on OP is altruistic, so I stepped in. Sorry if there was any confusion.

  4. #64
    smieglitz's Avatar
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    Quote Originally Posted by Stephen Benskin
    ...Didn't the edge also get developed to a CI 0.56? What about shooting a gray card? According to Sandy, a scene without a contrast range can't have a slope so it can't be developed to a given CI. Can a gray card be developed to a given CI? Of course. Can you determine CI with blank film of a single shot of a gray card? No, of course not. Is the blank film example a silly, bad example? Yes, but it also makes sense if you look at it a certain way. It's a thought experiment...
    Stephen,

    Again I would stress that the key to understanding this is to realize that developing for a certain CI is not the same as developing to a certain CI. The CI may be a measure of development, but it is dependent on the presence of an exposure range. That range must be present in order to make the measurement. When you simply have a blank, you have no range and no CI. If you have a blank and a gray card exposure you then have a range (0 exposure units and whatever exposure was given to the gray card) and thus can make the measurement in question and report it.

    Put yourself in the position of an absolute novice trying to understand how a blank frame could have the same contrast as a properly exposed and developed scene. It just doesn't make sense unless you realize that one statement implies an attempt to do something while the other represents a measurable result and an actual achievement. How does the novice come to properly realize the concept until a lucid explanation is offered ?

    And now you've sparked my curiosity. Can you explain the relationship between "statistical flare" and contrast index? How is statistical flare determined and related to the CI measurement?

    Joe

  5. #65

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    Quote Originally Posted by Stephen Benskin
    Not only is all of this wrong, the part on Ilford’s average gradient method suggesting a higher EFS approaches gibberish. These are methods to determine contrast – not speed. Joe’s post that Sandy is referring to has much more truth to it, but he doesn’t go far enough.
    Stephen,

    As I noted in the the part of my message that you quoted my reference for the description of the two systems was Davis. I have seen a different explanation of th Ilford G-Bar method that does indeed show that an arc is not involved in the determination of the Ilford G-Bar method so I will have to conclude that the plotting method I used to compare results of specific film tests with CI and G-Bar was faulty, at least as it regards my findings with G-Bar.

    Having said that I will say once again that the idea that you can have CI without exposure is simply inaccurate and you do yourself no favors in trying to defend something that silly, even as a "thought experiment."

    And one more thing. You wrote: "According to Sandy, a scene without a contrast range can't have a slope so it can't be developed to a given CI."
    Did I really say this? If so, would you please point me to it because I don't remember saying anything like this and can not find it anywhere in this thread.

    Sandy

  6. #66
    smieglitz's Avatar
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    Quote Originally Posted by Stephen Benskin
    As for Sandy’s conclusion that there is no distinction between the two methods…well, that has just been shown to be wrong. In a recent statement by Joe, he said "several of us have tried to be helpful and genuinely assist the thread originator with his question." How does Sandy offering bad information as fact and not opinion do that?

    And Joe, I wasn't trying to bait anyone. I simply don't believe ganging up on OP is altruistic, so I stepped in. Sorry if there was any confusion.

    Stephen,

    I don't believe we were "ganging up on OP". We both took issue with the same statement he made. We both indicated which part of his posts we took issue with and both asked for a clarification from him. The tone of this discussion has been civil. I don't think either of us is out to discredit him nor have we tried to. We've given him the opportunity to make a contribution and I believe he has finally done so which I've acknowledged.

    Personally, I have a limited knowledge of the concepts involved in this discussion of CI and sensitometry, but I don't believe I've spoken in error. If I have, by all means point it out as I'm eager to learn.

    I've also found Sandy King to be quite helpful, altruistic, and to the best of my knowledge , accurate in his explanations on a variety of topics over the years I've been in contact with him. In a recent thread I participated in with him concerning film choice and development (FP4 vs HP5), he clearly declined to make a pronouncement when he did not have the experiential data to back up a claim or prediction. This reveals integrity on his part. Whether he is in error or not on the points you've indicated, I'm not able to judge but I suspect he will do his homework and reply appropriately.

    You know, there is always someone smarter or better informed than any of us. I think this thread indicates that everyone involved has a different level of understanding of the concepts. We've pretty much been talking theory while the intent of the original question was probably asked with a more practical aspect in mind. I think all of us would do well to share our practical experience as well as whatever theoretical knowledge we may have on the subject. If we do so, everyone will benefit from it and we may all learn something.

    I haven't inquired to this point but I'm genuinely curious as to why we might prefer different methodologies. I assume OP, if he is MS, has found a way of working with his Leica and his darkroom procedures that gives him results he is happy with for the type of subject he chooses to investigate. I understand his rejection of the ZS, but I don't understand his vehemence against it or the majority of its practioners. (I do get the dittohead aspect of some of the ZS followers BTW.) I'm sure Sandy continues his investigations into methodologies that suit his style and subject matter too. His continued research into pyro and the PDN system bears that out. I'm somewhere very much removed from either and certainly not in the middle of some continuum. I know of noone else into the same things and using the same equipment for the same purpose as I do. I'm glad I've studied the ZS and read Davis, and Mortensen, and Zakia and King, and Kodak and Ilford, etc., because it all has helped me.

    Practically, I use (what I've found as a result of this thread to be) a simplified version of Kodak's CI for my work. I can relate it to my practice and to the other systems. CI is a useful concept for me yet I've never even seen a commercial control strip little less developed one. The Zone System is not really helpful to me in the field because of my specific interests. Yet, I realize that is not the case with everyone. I'm probably about as accurate judging exposures and development schemes as I would be with a meter. (Once had a SEI meter BTW.) I pretty much have to wing it in the field but my guesses are based on previous tests (and these might be ring-arounds or ZS) and observations. I'm more confident looking at the sky and the shadows than I am at measuring luminances and reading instruments.

    So I guess my point is to share what you know, take what you need, and leave the rest. I think we all have the potential to contribute something meaningful and I hope that spirit guides us in our interactions with each other.

    And I am so looking forward to this gray veil of winter to finally lift (in the northern hemisphere at least) so I can get back to photographing what I want and stop spending so much time online.

    Cheers,

    Joe

  7. #67
    Stephen Benskin's Avatar
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    Quote Originally Posted by smieglitz
    Stephen,
    And now you've sparked my curiosity. Can you explain the relationship between "statistical flare" and contrast index? How is statistical flare determined and related to the CI measurement?

    Joe
    Flare isn't involved with the determination of Contrast Index, but it does influence everything else. For instance, ISO exposure method incorporates flare into it's determination (flare adds an extra stop of speed under average conditions). With Contrast Index, you want to determine the proper CI for the given conditons. Of course, you determine the desired negative DR with the testing of paper. Most people don't realize that matching the negative to the paper isn't as solid a concept as they think. Jones also did the definitive work on this subject and he concluded, “because of the influence of the brightness distribution and subject matter in the scenes photographed, an accurate prediction cannot always be made of the exposure scale (LER) of the paper which will give a first-choice print from a negative of known density scale (DR)… But what other course is there to follow? Either we must make the best of a somewhat imperfect relationship or face the prospect of having no criterion whatever for choosing the paper contrast grade.”

    The LSLR is determined with your exposure meter, but more importantly is the illuminance range at the film plane. That is really what you are processing for. The problem is flare is next to impossible to determine in the field. In cases such as this, it's best to estimate using a value for the average conditions.

    The average luminance range derived from 126 sample scenes used in a study by Lyod Jones at Kodak was 1:160 (2.20 log units), with a standard deviation of 0.38. This means that 68% of the scenes fell within a 2½ stop luminance range of the average, while 95% fell within a 5 stop luminance range. The luminance ranges of the scenes tested were from a minimum 1:27 (1.43 log units, approx. 4⅔ stops) to a maximum 1:750 (2.88 log units, approx. 9½ stops).

    The apparent scene luminance range changes within the camera do to the influence of flare. Flare is non-image forming light created by any lens and camera system. Reflections between lens surfaces, lens-to-air surfaces, the sides of the lens (barrow), and the inside of the camera all help to create flare. What flare does is to introduce additional exposure to the film. Flare has a greater influence in the shadow exposure values than with the highlights. This effectively reduces the apparent luminance range of the subject at the film plane. The average value of flare for the statistical average luminance range is 0.34 for large format lenses and 0.40 for small format lenses. The flare effectively reduces the luminance range from 7⅓ stops (log 2.20) to a 6 stops (log 1.80) within the camera (2.20 – 0.40 = 1.80). Photographic processing is then based on the camera image of 6 stops and not the scene luminance range of 7⅓ stops.

    Instead of plugging in 2.2 for CI determination, you plug in 1.80. The equation is expressed as:

    CI = Desired Negative Density Range / LSLR - Flare

    For a grade 2 with a diffusion enlager, it becomes: 1.05 / 2.2-0.40 = CI 0.58

    Projecting it for difference Luminance Ranges and three different flare models:

    Dev_____LSLR____No Flare____Fixed Flare____Variable Flare
    -2______2.80______0.30_______0.44____________0.48
    -1______2.50______0.42_______0.50____________0.53
    N_______2.20______0.48_______0.58____________0.58
    +1______1.90______0.55_______0.70____________0.66
    +2______1.60______0.66_______0.87____________0.75
    +3______1.30______0.81_______1.17____________0.88



    Part of the fun is that flare tends to change with differing LSLRs. It increases as the LSLR increases and decreases as the LSLR decreases. You can see how it tends to temper the necessary range of processing. The question is which is the most accurate. Any scene can produce a variety of flare depending on the size and distribution of tones. This is a variable that, for the most part, cannot be controlled.

    One thought comes from Jones' observations about the matching of the negative to the paper. Jones concluded that, even though matching the negative DR to the paper LER isn’t a perfect criterion, it is good enough to produce quality images in most situations, or at least with a slight contrast adjustment. Jones also found a few exceptions to the DR / LER criteria, “for the soft papers, the density scales of the negative (DR) should in most cases exceed the sensitometric exposure scale of the paper (LER), whereas, for the hard papers, the density scales of the negatives should in most cases be less than the sensitometric exposure scale of the paper (LER).”

    Are these exceptions enough to cover the variable flare method if or when it falls short? My personal feeling is to introduce another method which I call the "practical flare method." It basically is the mean between the fix 0.40 flare model and the variable flare model. I've attached a graphic depiction of the various flare methods.

    I hope this is what you are looking for.

    Sandy, I think I got it from:

    "But a film that has received no exposure can not be developed to a CI of anything other than 0.00 because it can never, for all practical purposes, have any slope."
    Attached Thumbnails Attached Thumbnails Flare examples APUG.jpg   Film Paper Dev Method.jpg  
    Last edited by Stephen Benskin; 04-08-2005 at 03:01 AM. Click to view previous post history.

  8. #68

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    Quote Originally Posted by Stephen Benskin

    Sandy, I think I got it from:

    "But a film that has received no exposure can not be developed to a CI of anything other than 0.00 because it can never, for all practical purposes, have any slope."
    .
    Quote Originally Posted by Stephen Benskin

    Sandy, I think I got it from:

    "But a film that has received no exposure can not be developed to a CI of anything other than 0.00 because it can never, for all practical purposes, have any slope."
    Stephen,

    But that is not at all the same as what you claimed I said, which was, “According to Sandy, a scene without a contrast range can't have a slope so it can't be developed to a given CI.

    Those are two very different statements, as I think any reasonable person would agree. I suppose we could parse the language to say that are ways to reach the same result with sheets of unexposed and exposed film, say for example by exposing a sheet of film to a scene in absolute darkness.
    But even the result will be in both cases be negatives with no CI, or a CI of 0.00 if you will.

    But for whatever reason or purpose you misquoted me and misrepresented what I said. And that is a plain and simple fact.


    Sandy

  9. #69
    smieglitz's Avatar
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    Quote Originally Posted by Stephen Benskin
    ...we must make the best of a somewhat imperfect relationship...
    Ain't it the truth?

    Thanks for the explanation Stephen.

    Joe

  10. #70

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    Stephen, I have no idea why you have taken it to become the defender of the weak on this forum, but it does not do your reputation any good to try and defend a position that is wrong by drawing all these graphs and writing page long disertations based on a false concept.

    The simple fact is that gamma average or CI (whichever you like to use) is defined by two points that have to be present. Remove any of those two points and you no longer meet the definition of CI. In the case of the blank film exmaple you are actually removing both points that define CI, the one above b+f and the one that defines development. Anybody that knows a little of sensitometry will know this is just plain wrong.

    According to you and il duche bag. if I am cooking a chocolate souffle it is the same if I just crack an egg, throw a piece of chocolate and put both in a dish and stick it in the oven to beating an egg white with sugar, carefully folding melted chocolate into the whites and pouring this mix into a container that has previously been greased with butter and then carefully put into an oven at 350 ºF. Trust me, the results and the taste will not be the same......

    On the subject of SBR, it would be nice of you actually quoted the author correctly before you tell us all that it is wrong and outdated. What Davis is talking about is illuminance range not luminance as you stated. There is a difference you know.

    As to why people are beating on Il douche bag, this thread is a perfect example of his kind of confrontational attitude that does not acknowledge any other opinion than his own. The author of this thread asked a simple question in hopes of getting answers that will help him understand how to use his recently acquired densitometer to better control his process. Instead of offereing helpful suggestions his responses are on the line of "why did you get a densitometer? it has no use." While he is entitled to his opinion, invariably every time he participates in a thread it become a shit slinging fest that at least in this forum is not tolerated by the rest of the membership.

    It would have been nice that with all your knowledge of sensitometry you would have actually answered his question and help the author of this thread instead of becoming the defender of the weak and downthroden. So far you have not written a single sentence that would help the person who initiated this thread.

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