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  1. #71
    Stephen Benskin's Avatar
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    Quote Originally Posted by Xmas View Post
    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
    Pretty much. The third of a stop basically comes from factoring flare into the exposure. It's easy to think that the 1/3 stop comes from the speed equation being 0.80 / Hm instead of 1 / Hm, but it doesn't. This is in Safety Factors also.
    Last edited by Stephen Benskin; 05-02-2014 at 07:45 PM. Click to view previous post history.

  2. #72
    c6h6o3's Avatar
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    Quote Originally Posted by markbarendt View Post
    Just for giggles can we have some context for that rating.

    Developer?
    In comparison to manufacture's specs are you using minus development, stand...?
    Are you "zoning"? If so details?
    Subject matter?
    Spot meter or incident?
    Are you using old Petzvals or newish multicoated lenses?
    Is part of that rating a safety factor?

    My intent here is not to put you on the spot c6h6o3, but to help marciofs understand how you made your choice and at least some of considerations that go into the decision.
    Developer: Harvey's 777 OR ABC Pyro OR Pyrocat HD 1.5:1:175.
    I use the Zone System. I rate sheet film at 200, but place the shadows on Zone IV. So by Adams' philosophy I'm rating at 100. I meter for roll film at 100 and take incident readings. Therefore the answer is 'both'.
    Subject matter is anything that strikes my fancy: portraits, landscapes, abstracts.
    For sheet film I use a Nikkor 210mm large format lens, or an uncoated 12" f6.3 Dagor from 1911, or a 19" APO Red Dot Artar. My rollfilm camera is a Hasselblad. (250mm Sonnar, 150mm Sonnar, 80mm Planar, 50mm Distagon). So again the answer is 'yes to both'.
    I don't know what you mean by 'safety factor'.

    My point, both here and in the post you responded to, is that your film rating is an independent variable. "Expose for the shadows". Once you do that it's development that determines everything else about your negative. The old saw is "Develop for the highlights". But I develop for highlights, overall contrast, microcontrast in the midtones, all kinds of things depending upon what kind of negative I'm after.

    So I reiterate: The correct film speed is whatever gives you sufficient shadow detail in your prints.
    Jim

  3. #73
    Stephen Benskin's Avatar
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    Quote Originally Posted by c6h6o3 View Post
    My point, both here and in the post you responded to, is that your film rating is an independent variable. "Expose for the shadows". Once you do that it's development that determines everything else about your negative. The old saw is "Develop for the highlights". But I develop for highlights, overall contrast, microcontrast in the midtones, all kinds of things depending upon what kind of negative I'm after.

    So I reiterate: The correct film speed is whatever gives you sufficient shadow detail in your prints.
    You're talking about exposure and EI, not film speed. Conflating them can create a lot of confusion and misunderstanding.

  4. #74
    Photo Engineer's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Pretty much. The third of a stop is basically comes from factoring flare into the exposure. It's easy to think that the 1/3 stop comes from the speed equation being 0.80 / Hm instead of 1 / Hm, but it doesn't. This is in Safety Factors also.
    And this is why I use 320 for a 400 film when doing critical work.

    PE

  5. #75

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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.
    I'm not sure this is correct. My understanding of the print studies regarding shadows is that some of the toe is used. This is quite different than saying "unimportant".

    And while it is probably true you won't typically hear Zone System users say shadows are unimportant, it is also probably true they don't know what kinds of shadow contrast they are actually getting. As you know it quite a leap to imply tone reproduction from a simple fixed density speed point.

  6. #76
    Stephen Benskin's Avatar
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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.
    Bill, you're under selling the importance of the first excellent print test. The speed method resulted from the first excellent print test was the first to link exposure criteria to perceived print quality. W.F. Berg explains it very nicely in his book Exposure Theory and Practice, "In his book the whole of the exposure problem is treated from the point of view of obtaining a satisfactory picture; it has been stressed over and over again that the quality of the picture is the factor which decides what exposure should be given. This consideration outweighs all others when it comes to choosing the speed criterion, since on its choice, together with the conditions of the subject, will depend the camera exposure to be given.

    Thus all those speed criteria must be rejected which are based merely on a property of the negative material alone; unless and until it can be shown that this property is intimately liked with the quality of the print. Nevertheless, speed criteria are in practice invariably determined from the behaviors of the negative material alone. Where progress has been made in recent years in fixing a sensible criterion, it has been in the direction of linking print quality with the characteristics of the negative material...

    We consider as our next speed criterion that introduced by Jones and adopted both the American Standards Association and the British Standards Institution. With this criterion, we complete the circle which started from a purely academic linking of the speed with an almost entirely arbitrary property of the characteristic curve, then led us to the purely practical concept of speed, to end up with what appears to be the most successful attempt so far of connecting print quality with a characteristic of the negative material.

    Realizing that speed must be based on print quality, Jones decided to make a large number of exposures on a large variety of subjects on many negative materials and to submit the prints to a number of observers who were asked to judge the print quality. These prints were made on a grade of paper best suited to the negative in hand, i.e. on hard paper for underexposed negatives of low contrast, and on medium or even soft paper for the more correctly exposed negatives…

    The final step was to link this criterion with a property of the characteristic curve. The point was to find that characteristic of the negative material which best tied up with the exposure necessary to yield the first excellent print."

    Not sure where you found that the study concluding some of the shadow detail wasn't important. Jones' conclusion kind of contradicts that.

    No one said the Zone System speeds were based on the fractional gradient. There's no indication Adams was aware of it or would understand it if he was. What he was trying to do is to come up with a testing method that can be done by the photographer that will approximate the ASA film speed. Which he did. My argument has always been about understanding the test. I don't care if the Zone System produces an almost universal 1/2 to 1 stop slower results than the ISO speed. Just don't call it "true" or "correct" speed. Personally, I believe the reason there is so much emphasis on determining a personal EI with the Zone System is because you can't test for the aim contrast without it. Otherwise, I can't see the purpose of doing such an imprecise test.

    Finally, I'll just touch on this point for now, the speed point isn't necessarily where the shadow exposure is intended to fall. The fractional gradient point is approximately one stop below the ISO speed point, yet the pre 1960 speeds were twice as high as today. The reason why the density of 0.10 over Fb+f was chosen for the speed point in the current ISO standard was not because it represents the minimum useful exposure, but because it is easy to find.

  7. #77
    Stephen Benskin's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    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.
    Could you elaborate on the disconnect that you've found? Meanwhile I'll work on addressing your questions. I can tell you that most of the answers can be found in the Simple Methods paper.

  8. #78
    Stephen Benskin's Avatar
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    Last page (part 2) of Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials.

    Simple Methods last page.pdf

  9. #79
    Bill Burk's Avatar
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    I love the "First Excellent Print" study and I did not mean it any ill will when I accused it of saying some shadow is unimportant - that's just my take. I figure since it puts you down on the toe a bit where there's little separation - and when you print, the paper curve is also in its shoulder where there is little separation - you get double compression. But it looks good to viewers. And what looks good is EXTREMELY important, it's a great baseline for the ISO standard.

    Zone System, on the other hand, stresses an educational approach to illustrate the principle "expose for the shadows and develop for the highlights." This is a fundamental principle, but it leaves Zone System on the rejected side of the standards because its aims are arbitrary, based on a point where you can see separation of tone in the shadows on the print.

    They are two different ways of deciding the minimum exposure.

    The "First Excellent Print" method: Minimum is the least where the whole print looks excellent.
    The "Zone System" method: Minimum is the least where you can see detail in the shadow.

    I amuse myself exploring these two different definitions of quality, and I am not surprised they result in different speed ratings for the same emulsion.

  10. #80
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Last page (part 2) of Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials.

    Simple Methods last page.pdf
    Looks like I am wrong to associate Print Judgment Speed with 0.3G speed. This compares them as three different criteria.

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