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  1. #31

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    Quote Originally Posted by Jorge
    If you wish, you can then plot SBRs against average gamma to obtain a correlation.
    OK - sorry for my misuse of terms, But this is what I was doing. It also shows that SBRs do correlate to average gamma, and therefore average gradient, and even CI.

  2. #32

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    Quote Originally Posted by jdef
    Jorge, I'm surprised to see you respond, I thought I was surely on your ignore list. As I've said, SBR values can be extracted from curves derived from stepwedge prints. The stepwedge itself represents the luminance range of a theoretical subject. Don's definition doesn't recognize that the stepwedge represents a theoretical subject, the luminance range of which does not need to be metered, because it is a known value which can be measured with a densitometer.



    Are you saying that the SBRs derived from these curves are all the same? If not, then they must represent a range.



    I can target any value I like. If I develop a test negative from which I derive an SBR of 5, but want to determine the appropriate development for an SBR of 7, I can develop a second test negative for a period determined by extrapolation, guesswork or voodoo that I reason might result in an SBR of 7. Wether or not I achieve the targeted SBR is irrelevant, the point is that I targeted that value.

    Jay

    Well yes you are in my ignore list, but in this case I was made aware of your erroneous post. Your first paragraph is enterily wrong. You cannot obtain a range of SBRs from a step wedge test, what you obtain is a range of average gammas. As I said, you can the plot averag vs SBR for your specific tests. IOW, an SBR of 6 is the same for you, me, Kirk or anybody using the BTZS. Development of an associated average gamma to that SBR is specific for each user.

    If you are going to correct people it would be nice if you at least learn the terms as they have been explained by the creator of the system.

  3. #33

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    Quote Originally Posted by Kirk Keyes
    Jorge, thanks! I should have mentioned my paper scale - sorry. I use 1.05. Could you re-crunch them?

    Kirk
    SBR 2.6
    Average Gamma 1.33
    film speed 250

  4. #34

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    Quote Originally Posted by Kirk Keyes
    I agree completely. Anytime you are shifting tones away from a direct approximation of the original scene requires interpretation. Never said otherwise.

    Thanks for this technique - this is what I'm asking about. However, I'm not sure about it. I had no shadow areas with the sand pattern or the rock art. I guess I'm not visualizing what you are suggesting to do - here's what I think you are suggesting:

    1) I have a subject with no shadow areas, one that is of low contrast.
    2) Take a reading in the sunlight with the incident meter at the subject.
    3) Take a second reading in the shade of my hand.
    4) Subtract the two readings.
    5) Exposing with the average reading.

    This seems like a kludge. Is there a basis in the BTZS method for this, or just something that has been found to work fairly well? It seems like you could get a lot of variation based on how much you cover the meter sensor with your hand.
    The comment about interpretation was simply stated as a point of reference, not to contradict anything you previously said.

    As for the technique I suggested here are some things to think about.

    1. Unless you are photographing a flat object, such as a gray scale, objects in nature will always have shadow values. You may not be able to measure them because of their size, but they exist nevertheless. Even rock art has shadow values, say in the crevices between the rocks, between the lines that outline the image, etc. You may not be able to meter the shadows, either with a reflected or incident reading, but they are still there.

    2. If all of the areas of the subject are illuminated by the same light, say the sky, it will not make a lot of difference whether the cone of the meter is completely covered or not, but you do want to make sure that the cone does not see the sky. This should provide a very reliable base to calculate the SBR. Have you ever noticed how little shadow values change with incident readings with the sun out or the sun obscured by clouds? Some, but very little. I think the same rationale applies here. Whether you entirely cover the cone of the meter, or only partially cover it, there will not be a big difference in the reading.

    3. How well does this method of incident metering in flat scenes work? In my experience surprisingly well. The subtext of some of the messages appears to suggest that this kind of scene is difficult or impossible for BTZS incident metering. My own experience suggests otherwise.

    Your resume of my suggested technique is correct as to the method for determining exposure, but not for determining SBR.

    Here is what I suggested. The scene is this. You use your incident meter and take readings, but regardless of where you point it you get the same EV reading, which suggests an overall SBR of 5. To compensate, do this. Record the SBR as 5 and then take another reading, covering the cone of the incident meter with your hand so that it does not see the sky. Record the EV reading and subtract it from the value that give you the SBR of 5 suggested earlier. This will give you the adjusted SBR that will be used to determine time of development.



    Sandy

  5. #35
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    "Thanks for this technique - this is what I'm asking about. However, I'm not sure about it. I had no shadow areas with the sand pattern or the rock art. I guess I'm not visualizing what you are suggesting to do - here's what I think you are suggesting:"

    Kirk,
    Phil goess into this in his BTZS Lite. Metering for 2 dimmensional objects. I think that may help you here.
    "EVERY film and paper is good .......... for something"
    Phil Davis

  6. #36

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    Quote Originally Posted by Kirk Keyes
    I agree completely. Anytime you are shifting tones away from a direct approximation of the original scene requires interpretation. Never said otherwise.



    Thanks for this technique - this is what I'm asking about. However, I'm not sure about it. I had no shadow areas with the sand pattern or the rock art. I guess I'm not visualizing what you are suggesting to do - here's what I think you are suggesting:

    1) I have a subject with no shadow areas, one that is of low contrast.
    2) Take a reading in the sunlight with the incident meter at the subject.
    3) Take a second reading in the shade of my hand.
    4) Subtract the two readings.
    5) Exposing with the average reading.

    This seems like a kludge. Is there a basis in the BTZS method for this, or just something that has been found to work fairly well? It seems like you could get a lot of variation based on how much you cover the meter sensor with your hand.
    You are absolutely correct, as I mentioned before here is where experience counts. In the same way that many of us found in the ZS that placing the shadows in zone III many times resulted in shadows without detail, the way you place your incident meter counts a lot.

    Once again and as a last post, if you check your curves when you are making your measurements you can use the effective film speed given by them when you decide to use lower than 5 SBRs, but knowing which lower SBR number to use is a crap shoot. Given that variations in film speed are very small at this range of expansion, presumably using an SBR of 2.5 or an SBR of 3 amounts to a very small error in exposure.

  7. #37

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    Quote Originally Posted by jdef
    Jorge, I'm surprised to see you respond, I thought I was surely on your ignore list. As I've said, SBR values can be extracted from curves derived from stepwedge prints. The stepwedge itself represents the luminance range of a theoretical subject. Don's definition doesn't recognize that the stepwedge represents a theoretical subject, the luminance range of which does not need to be metered, because it is a known value which can be measured with a densitometer.

    I can target any value I like. If I develop a test negative from which I derive an SBR of 5, but want to determine the appropriate development for an SBR of 7, I can develop a second test negative for a period determined by extrapolation, guesswork or voodoo that I reason might result in an SBR of 7. Wether or not I achieve the targeted SBR is irrelevant, the point is that I targeted that value.

    Jay
    Jay,

    Normally I would not choose to respond to your quest for individuality. However it appears that you made assumptions that are erroneous. The first is that you assumed that I did not consider the density of the step tablet. I found nowhere that I have stated any thing of the sort.

    Beyond this I will no longer choose to discuss this subject with you. It is quite apparent that you have adapted the BTZS to your own frame of reference. That you use it in ways that most of us don't. It is because of this that you and I can not communicate about BTZS as it was formulated and presented in a clear and concise manner.

  8. #38

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    Quote Originally Posted by sanking
    Or let me put it another way. OK, so you decide to "develop your film to a given CI", but after development you discover that the CI is different from the one to which you "developed your film."

    OK, to what CI did you really develop your film? And is that question different than asking, "to what CI was your film developed"? Sandy
    Sandy the questions in your post here indicate to me that you (and probably many others) are having a disconnect between the act of measuring the CI of a piece of film, and developing that piece of film to a predetermined CI. They are two different acts.

    Quote Originally Posted by sanking
    Or let me put it another way. OK, so you decide to "develop your film to a given CI", but after development you discover that the CI is different from the one to which you "developed your film."
    Good question! I'm certain that happens almost every time you, or I, or anyone develops film. You've made a measurement in the field of your subjects luminance range, be it with the Zone System, BTZS, or any other system that you have devised to measure it. You go back to your darkroom, unload your film, and get ready to process it. In the past, you've done some tests and you have a table or graph that you have associated development times to your subjects conditions. So based on that measurement of the subject luminance range, you pick a developer time, temp, method of agitation... By doing this, you have decided to develop your film to a predetermined level of overall negative contrast. You then go and process that film. You do things as carefully and consistantly as possible, and because you are a good darkroom technician, you try to minimize any influences on the development process. Afterall, if you goof, you will most likely not achieve that desired level of development, your target CI.

    The key here is to have good process control - and I don't mean "process" as in "film processing", I mean it in the quality control sense. All your development times are based on measurements that have been made under a (hopefully) controlled environment and set of conditions. The accuracy of your time measurements, the precision and readability of your thermometer, the strength and age of your developer, its actual pH, the remaining buffering capacity..., your ability to agitate your film in a consistent manner, the ratio of film to developer volume, the total amount of silver that was exposed on the sheet. All these things and more affect the final amount of development your film recieves - they will affect the actual CI.

    Depending on how well you can do these things, you should be able to get pretty close to your desired amount of overall negative contrast. Many of us here may actually not be able to, someone that is using a large dip and dunk processor will probably be able to hit the target CI. Especially if they have calibrated the system recently.

    Do you need to have measured the actual CI you set out to hit? Maybe not. Maybe one guy had a target CI was 0.60, and he did run a control strip with the run and with 5 runs got measured CIs of 0.59, 0.63, 0.58, 0.70, and 0.61. Maybe the guy with the dip'n'dunk can consistently get CI results centered between 0.58 and 0.62. And I mean consistently, centered around 0.60. The dip'n'dunk guy would be in better control than the other guy. The guy with the dip'n'dunk can come to the reasonable conclusion, that when the dip'n'dunk machine is in control, he can get a CI of 0.60, or more precisely stated 0.60+/-0.02. The other guy, cannot be as confident in his results, but even he has the beginning of some statistical basis to make a claim that he can get hit a CI close to 0.60 (the actual average was 0.62, but his standard deviation (0.05) is not that good). He needs to work on his process control.

    I hope you haven't fallen asleep yet, as I'm ready to bring it together.

    Quote Originally Posted by sanking
    OK, to what CI did you really develop your film? And is that question different than asking, "to what CI was your film developed"? Sandy
    It is only really different if you do not have very good process control. If you do have good process control, you can say, with good confidence, that you did develop any particular film to some particular CI. If you have poor process control, then you may have an idea of a probably range of CIs that were achieved.

    So ultimately, you will have to decide if you have good process control. If so, you can make these conclusions. And you don't need to run a control strip alongside every piece of film, either.

    If you can't get consistent, then it's probably better not to.

    Please note at no time in this did you have to have a full range of exposed tones on any of the film that you processed (except the ones that you actually used to make the CI calculations) - all the film will have a CI of whatever CI the run was at. Even if the film was blank...

  9. #39

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    Quote Originally Posted by jdef
    Jorge, you're reaching. We are discussing SBR values derived from film curves, not SBR values as metered in the field. There is a difference. From BTZS fourth edition:

    "..find the SBR for each curve by measuring the horizontal distance between its IDmax and IDmin, as illustrated in Figure 4-12. Then label each curve with its SBR in stops, as shown." The accompanying illustration shows a family of curves with a range of SBRs labeled as follows:

    3.7
    4.7
    5.8
    7.4
    11

    (Don, those are SBR values in tenths, used by someone familiar with BTZS)

    The above is a range of SBRs derived from film curves. You can qualify that any way you like, but that's what it is, according to Phil Davis. You can go back to ignoring me now, if you like.

    Jay
    Yeah, I will go back to ignoring you as apparently you did not understand what you were reading. What were you plotting in the paragraph you mention?

    You are plotting a curve to find out average gamma, which you can then associate to a SBR value that you will obtain when taking a photograph.

    My intention was to clarify this for those who are reading the BTZS and want to learn it correctly. I have no intention of continuing to argue with someone who 2 years ago was asking "what is azo paper?" and now is a master of all things photorgaphic and even names developers after himself....Unlike you, what I know, I know well, but I am not an expert on everything.....

  10. #40

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    Quote Originally Posted by Jorge
    SBR 2.6
    Average Gamma 1.33
    film speed 250
    Thanks Jorge, Even higher than I thought!

    By the way, your film CI is probably off, as I did not give you any exposure information, so I'll take that calculated result with a big grain of salt. I most likely did not meet the exposure conditions that Phil recommends.



 

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