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  1. #61

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    Quote Originally Posted by Bill Burk View Post
    Sorry to bring up a new argument in the conclusion... But the first debate I won in high school was because I had a suprise argument.

    The Delta-X Criterion, which I use for my own speed determination (so I subscribe to it but I want to explain something)... is based on the agreement that 0.3 Gradient is the appropriate speed point... Based on the study of The First Excellent Print.

    Zone System speeds are NOT based on the study of the The First Excellent Print. So there is no reason except coincidence that the speeds even closely relate.

    The First Excellent Print is based on people who viewed prints and pointed to the ones they liked. Built into this study is a Standard Observer's Opinion that "some" of the shadow detail is not important.

    The biggest difference between this and the Zone System is... You will never hear anyone who uses the Zone System saying that shadows are not important.
    Sorry shadows are not important if you are shooting slides.

    If you are shooting negatives if you get zone 1 below the halide fog it is not present so no detail.

    If zone1 is into the toe it will be more difficult to print unless you like dark prints with compressed shadows.

    Some people do like that and it can add emphasis.

    Until 1960 the box speed had a safety factor of 2.5 stops, post 1960 this was reduced to 1.5.

    HP3 boxes changed from 200 ASA to 400.

    Some manufacturers don't put the ISO speed on the box, eg Forma and I'm picking Forma as a good example.

    Forma as well provide a data sheet for each film type with the 'ISO' speed for developers you might use like eg DK76 as little graphs of fog, contrast and speed and temperature.

    If you look at the graphs it tells you a lot even if you are never to use Forma.

    Id already discovered that the Formapan 100 was nearly as fast as the 400 before I looked at the graphs. I should have looked at the graphs first.

  2. #62

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    Quote Originally Posted by Stephen Benskin View Post
    ... It's a very common misunderstanding. Film speed isn't determined by density because negative density by it self isn't relative to print quality. Film speed is determined by gradient. The fixed density of the ISO standard is a short cut to determining the fractional gradient point. As per Nelson, the fixed density method is only accurate when the contrast falls within the ISO contrast parameters. Otherwise you need to plug ΔD and Δlog-H into the Delta-X equation because with increased and decreased negative development, the fixed density method is less accurate. You're probably conflating it with how an increase in film density usually is accompanied by a higher gradient. This isn't always the case and definitely not to the same degree in different film types. This is all explained in Simple Methods of Determining the Fractional Gradient Speeds of Photographic Materials by C.N. Nelson and J.L. Simonds. If the OP really wants to understand what the REAL ISO is about, this is the paper.

    As for a personal EI, whatever makes you happy.

    The statement that very manufacturer deciding for themselves what the contrast for the standard should be is patiently wrong. The contrast parameters are clearly defined in the standard. Any variation and the ISO prefix cannot be used.
    Stephen,

    Obviously I'm working from an over-simplified model and using the terminology imprecisely...

    But, for the sake of clarification, when I develop, say N-2 in order to accommodate a rather high subject brightness range, am I not changing the gradient and therefore the effective speed of the film? Or would you say that this is outside the parameters of ISO testing standards and simply does not apply?

    If the latter, then what would you call the E.I. I need to use for N-2, simply E.I.? Is that not somehow "film speed" as well? "Effective speed" maybe?

    In any case, I feel we need some more easily-accessible and usable terminology to deal with changes in film response with different development schemes. Maybe you have some suggestions in this department that could be simply understood and utilized by non-specialists while avoiding conflation, ambiguity and confusion at the same time; something in Feynman vein.

    I never meant to imply that manufacturers can decide for themselves what the contrast standard for ISO determination is. However, it does seem that they can choose a developer, so there is no fixed standard in that department. Plus, there is a growing practice, especially for films designed to be used in low-light situations to have a number on the box, i.e., "box speed," that is not the true ISO speed (Ilford Delta 3200, et al.). This just adds to the confusion IMO.

    And, although I'll more than grant you the point that ISO is a strict and reliable value arrived at by rigorous methods, I still find a bit of a disconnect about how it is practically applied. Certainly, you would not advocate my using the film ISO as my basis for metering for an N-2 negative... or when using a developer that is known to not deliver full ISO speed. Or would you?

    I've spent a lot of time testing to arrive at development schemes that allow me to accommodate scenes with varying subject brightness ranges. While not completely quantified and constantly being refined, I feel I am much better off giving a tested and field-proven amount of increased exposure and reduced development for high SBRs and the converse for low SBRs. I have made Zone Rulers a lá Zakia and White for all my development schemes and am fairly confident using them. Should I really be questioning whether my testing method "is yielding reliable results"? Are the Zone System and BTZS tests unreliable?

    All the above in the spirit of refining my knowledge and technique with thanks in advance for taking the time to answer.

    Best,

    Doremus

  3. #63
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    Quote Originally Posted by Xmas View Post
    Sorry shadows are not important if you are shooting slides.
    Well, I wouldn't put it that absolutely. I don't think that Dunn & Wakefield or others say that shadows aren't important.

    What I might suggest is that with slides, that there are physical limits to what can be in the final artifact and that "we" need to decide what is most important.

    The testing Dunn & Wakefield used does show that most people find mid-tones and highlights more important but we do well to remember that we don't have to conform.
    Mark Barendt, Beaverton, OR

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

  4. #64

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    Quote Originally Posted by markbarendt View Post
    Well, I wouldn't put it that absolutely. I don't think that Dunn & Wakefield or others say that shadows aren't important.

    What I might suggest is that with slides, that there are physical limits to what can be in the final artifact and that "we" need to decide what is most important.

    The testing Dunn & Wakefield used does show that most people find mid-tones and highlights more important but we do well to remember that we don't have to conform.
    Well ok I'll give you subjective but I've never had a bride who liked her wedding dress other then right on the edge of burnt out on the projector screen.

    They never liked the 1/2 stop bracket if it was darker.

    Kchrome 25 was nice film.

    The grooms never minded or never said.

  5. #65

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    Quote Originally Posted by Doremus Scudder View Post
    Stephen,

    Obviously I'm working from an over-simplified model and using the terminology imprecisely...

    But, for the sake of clarification, when I develop, say N-2 in order to accommodate a rather high subject brightness range, am I not changing the gradient and therefore the effective speed of the film? Or would you say that this is outside the parameters of ISO testing standards and simply does not apply?

    If the latter, then what would you call the E.I. I need to use for N-2, simply E.I.? Is that not somehow "film speed" as well? "Effective speed" maybe?

    ...

    And, although I'll more than grant you the point that ISO is a strict and reliable value arrived at by rigorous methods, I still find a bit of a disconnect about how it is practically applied. Certainly, you would not advocate my using the film ISO as my basis for metering for an N-2 negative... or when using a developer that is known to not deliver full ISO speed. Or would you?

    ...
    Doremus
    Well if you just increase the development time you might increase the 'ISO' speed for your developer if the fog level increases less than the image level, otherwise the speed might be static or reduce.

    All you can be sure is your mid tones separate.

    The shadows and the highlights may be in toes and shoulders respectively.

    You need to pick soft working developers with log fog levels to allow a wider range of 'capture' and control if your sceanes are high contrast.

    For a while Ansell used D25 and a post alkaline bath or water bath. The D25 held the highlights the post bath the shadows if you were lucky.

  6. #66
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    Quote Originally Posted by Xmas View Post
    Well ok I'll give you subjective but I've never had a bride who liked her wedding dress other then right on the edge of burnt out on the projector screen.

    They never liked the 1/2 stop bracket if it was darker.

    Kchrome 25 was nice film.

    The grooms never minded or never said.
    And this is essentially what Dunn & Wakefield found as the norm, you are not wrong there.

    Yep, IMO most grooms just seem to follow the bride's lead on the photos.
    Mark Barendt, Beaverton, OR

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

  7. #67
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    This is the first part from one of the two key papers used in the decision to change the standard in 1960 and is where the Delta-X Criterion originates. C.N. Nelson and J.L. Simonds, Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials, Journal of the Optical Society of America, V 46, N 5, May 1956.

    part 1
    Approx Fractional Gradient Speeds.pdf
    Last edited by Stephen Benskin; 05-02-2014 at 10:31 AM. Click to view previous post history.

  8. #68
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    And the other, C.N. Nelson, Safety Factors in Camera Exposure, Photographic Science and Engineering, v 4, n 1, Jan-Feb 1960.

    Safety Factors pt 1.pdf

    Safety Factors pt 2.pdf

  9. #69
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    Quote Originally Posted by Xmas View Post
    Sorry shadows are not important if you are shooting slides.

    If you are shooting negatives if you get zone 1 below the halide fog it is not present so no detail.

    If zone1 is into the toe it will be more difficult to print unless you like dark prints with compressed shadows.

    Until 1960 the box speed had a safety factor of 2.5 stops, post 1960 this was reduced to 1.5.
    Bill kind of misrepresented the first excellent print test. I'll go into more details later.

    Xmas, the safety factor pre 1960 standards was 2.5 times, not stops. Afterward it was 1.2 times. You can read about it in Safety Factors in Camera Exposure that I've uploaded.

  10. #70

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    Quote Originally Posted by Stephen Benskin View Post
    Bill kind of misrepresented the first excellent print test. I'll go into more details later.

    Xmas, the safety factor pre 1960 standards was 2.5 times, not stops. Afterward it was 1.2 times. You can read about it in Safety Factors in Camera Exposure that I've uploaded.
    Hi Stephen

    Thanks, so in round terms there is not a safety factor in the ISO any more, or maybe 1/3 of a stop, given the ISO quantization.

    Noel



 

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