Examples of Different Speed Methods

Discussion in 'B&W: Film, Paper, Chemistry' started by Stephen Benskin, Jan 21, 2012.

  1. Stephen Benskin

    Stephen Benskin Member

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    I ran across these examples of speed methods for various film types (and one paper). This is the only time I've seen diagrams of non-pictorial films included. It's a bit dated, but I think it illustrates how the method of determining the speed is dictated by it's intended use.

    Standard Speed Methods 1.jpg

    Standard Speed Methods 2.jpg
     
    Last edited by a moderator: Jan 21, 2012
  2. jnanian

    jnanian Advertiser Advertiser

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    hi stephen

    is the graph showing photographic paper typical for all photo papers ?
    i have tested 20+ types/brands/grades of photopaper and they vary
    greatly in speed ... from asa 25 or 50 to less than 1
    ( asa relative to film speed, not the index numbers the companies give )

    thanks !
    john
     
  3. Stephen Benskin

    Stephen Benskin Member

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    John, today's speed point is the same, but the speed constant is different - S = 1000 / Hm.
     
  4. jnanian

    jnanian Advertiser Advertiser

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    thanks stephen !

    - john
     
  5. michael_r

    michael_r Subscriber

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    Stephen, thought I would ask you this question even though it is not necessarily the right topic, although definitely related. Why do so many people target a value for zone III when they test film for reciprocity adjustments? Why not aim for a repeatable zone I value, since .1 over base+fog is generally how most zone system users test for their working EI? Wouldn't it make more sense to target a constant EI for reciprocity corrections rather than zone III?
     
  6. Stephen Benskin

    Stephen Benskin Member

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    Michael, I didn't know they did. I would think that since latent image regression occurs most in areas of low exposure, using something like the 0.10 speed point would make sense.
     
  7. Bill Burk

    Bill Burk Subscriber

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    I'm guessing that choosing Zone III for reciprocity failure tests avoids the situation where the loss of speed leaves you too little information at the normal 0.1 speed point.
     
  8. ic-racer

    ic-racer Member

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    Others out there also. I can't find it right now but came across a definition based on minimum acceptable resolution on the Y-axis, with speed on the X-axis.
     
  9. michael_r

    michael_r Subscriber

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    I don't understand what you mean.

    Stephen, yes I've seen this method used in several high profile tests. For example, Howard Bond's well known tests have been quoted by many (even myself). He calibrated to zone III. I've seen zone III referred to in other writings on reciprocity as well. In fact, offhand I can't recall seeing any articles or books in which zone I was used as a reference point for reciprocity corrections.
     
  10. Stephen Benskin

    Stephen Benskin Member

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    I'd have to read those articles. Reciprocity only effect areas of low exposure (except for high intensity reciprocity, but that works differently). The principle is the same as latent image keeping as explained in the Gurney-Mott hypothesis. I don't remember much about chemistry, but here's an excerpt from Photographic Materials and Processes on reciprocity:

    "When exposures are made at low light levels, the efficiency with which the sub-latent images are formed on the crystal is low because of the tendency of the silver atoms to give up an electron and return to the ionic state. Further exposure allows a greater number of silver atoms to accumulate around those few sub-images that survive, but these sub-images are relatively stable."

    It seems to me that since reciprocity has a greater influence with lower exposure levels, and since the purpose is to define the film speed at lower exposure levels over a longer period of time, then the speed point would be a logical point of measurement.

    Again, I'd have to read the other people's reasoning in order to comment on them. But I frequently seem to be at odds with popular wisdom.
     
  11. michael_r

    michael_r Subscriber

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    Stephen, here's the Howard Bond test, often quoted and used to generate reciprocity formulas. I've gone through the tests in detail in the past, but just re-reading it quickly now, even in the intro paragraph he mentions the intent is to keep zone III constant.

    Perhaps the reason people disregard densities below zone III when testing for reciprocity corrections for current films is that reciprocity failure is much less "exposure-dependent" than it used to be - ie there is much less contrast effect in reciprocity failure than with older films because areas of low exposure respond in similar ways to areas of high exposure. This is also discussed in the article.

    http://www.phototechmag.com/index.php/archive/reciprocity/
     
  12. Stephen Benskin

    Stephen Benskin Member

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    Michael, thanks for posting the link to the Bond article. I’ve been able to skim through it a couple of times and I’m sure the results he got are fine. And while I haven’t done a thorough read, there are a number of observations I’d like to make about the testing.

    Bond never explains why Zone III is the aim exposure for the testing. He doesn’t address it in anyway. There’s no theory to support the choice. I don’t know about anyone else, but my first reaction is to ask why that point and why not another exposure or density point? He doesn’t even make an assumption why Zone III should be used. What would his results be if he tested a stop lower, or two stops lower? Are we to simply accept his choice of Zone III without an explanation? While I’m sure his numbers will yield acceptable results, there is no evidence that they are remotely representational of the film’s reciprocity.

    There are two other things that stood out. First is the testing exposure of 5 ½ stops above the metered reading (Zone X ½). I guess technically the exposure was keyed to Zone IX ½ and given another stop for close up compensation. His results are pretty much what I’ve written about (most recently in the Large Format Forum). It’s easy to calculate the film plane exposure when you are using a camera as a sensitometer. Basically five stops over the metered exposure point will produce about a stop less exposure than most of the these type of methods assume. I haven’t worked out the specifics of Bond’s testing, but on the surface, this appears to be the case.

    The other thing was the paragraph about camera flare. I had to go back and re-read how he was using the step tablet because I couldn’t believe that anyone would have a paragraph on flare (and creating a device to boot) if the test was contacted. And I discovered I hadn’t misread the testing procedures. The step tablet is indeed contacted. Not only contacted, but the target was a single toned white subject. This is about as flare free a test as one can get.

    How valid is the test? It’s questionable at best in my book, but I’m sure the results are good enough for photography work.
     
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  13. michael_r

    michael_r Subscriber

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    Thanks for your thoughts on this, Stephen. It has puzzled me for some time. The simplistic assumption I make is that since the shape of the curve for most current films does not change nearly as much with reciprocity failure as it did in the "old days", Bond and others reason that by maintaining a stable zone III density, the densities below also remain pretty much where they were as well. I don't know, but that's really the only logic I can find in the approach. But even still, why zone III and not zone II or I, after establishing EI with a zone I density in the first place. Zone III is usually an important value for most zone system users. But for it to remain that key shadow point for retaining good detail when reciprocity failure takes over requires that the densities below zone III remain the same as under normal reciprocity conditions.

    Anyhow, food for thought.

    Thanks again for the insight.
     
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  15. Stephen Benskin

    Stephen Benskin Member

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    Low level reciprocity only affects the lower luminance values. The reason why development needs to be reduced when compensating for reciprocity is because the higher values aren't affected by the latent image regression and build additional density with the additional exposure required to create adequate shadow density. The further the exposure is from the shadow, the less of an affect reciprocity has on it.

    What Bond needed to do was to first prove that the use of Zone III was the best point to test for reciprocity. He would then have a strong foundation from which to present his conclusions.

    I believe it's important to do a little critical analysis with any written material or claim and not just take the author at their word. There's too much argument from authority used in and around the photographic community and too many statements and claims made without any proof or supporting argument. I'm consistently tempted to simply reply "prove it" to many posts here on APUG. Ansel said it was so just isn't enough.

    I'm currently doing a little critical analysis of a few charts and graphs in the thread Hiding in Plain Sight. I think it would be a good idea to make it a common practice here to do more critical analysis of articles, graphs, information from websites, or photographic theories or concepts. Such discussions would be a welcome change from the ubiquitous what developer to use with what film threads.

    The Bond article is a good start. Too many of these types of articles tend to be heavily into the how to and light on the reason why. Shouldn't we be also talking about the why?
     
  16. CPorter

    CPorter Member

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    Why should you force feed a "why" analysis on someone else's results........if for yourself, that's fine.

    I have a camera and a step wedge-----and I have a text that I use that has taught me "how to" effectively carryout tests for EI. My tests have been hugely rewarding and have helped me improve my photographic abilities exponentially. "Why" should I let you try to convince me that I just don't really understand what it is that I am looking at? There is absolutely nothing wrong with "how to" as a point of departure for going forward and utilizing what you have learned for yourself. The results are put into practice that have yielded such good negatives, speaking for myself that is.
     
  17. michael_r

    michael_r Subscriber

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    Stephen, regarding low level reciprocity, one of the things Bond argues is that with current films reciprocity failure is much more linear than it once was, or may have been. He finds it is not as biased toward low luminance values as we think it is and so, surprisingly, he finds much less development compensation is typically required for long exposures - at least with the films he tested. He found the contrast increase during long exposures is actually minimal with these films. People often report that this is how enlarging papers behave when reciprocity failure kicks in - ie you need longer exposure times, but there is no significant increase in contrast. I'm not sure about any of this, but it's interesting.

    Regarding asking why, I think as long as we don't get too bogged down in levels of precision unattainable outside the lab, the discussion can definitely be interesting. Knowledge is a good thing. Personally I'd agree we tend to follow the technical writings of well known photographers too blindly. Mostly, things seem to work ok. But some writings really need to be challenged (in my opinion). Barnbaum's book is a good example, one I have criticized before on here. He might be a good photographer, but I don't think he "knows what he's getting" in his negatives. He's adjusted for all that with experience (perhaps without realizing it), but he shouldn't be writing about densitometry and the zone system. He's dead wrong about quite a few things.
     
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  18. Stephen Benskin

    Stephen Benskin Member

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    It's called a discussion or an analysis. Why do it? Because we are not sheep or robots. Following something blindly may be fine for some, but not everyone. Why should you feel the need to repress learning?:smile:

    Come on Chuck, don't get defensive over this. I'm sure you started with the standard Ansel Zone System test until you discovered the Schiffer test when you asked yourself why one may be better than the other. It's all just a matter of degrees. If you're happy with your the results of your test, great. Many people are happy with their results without doing any testing at all. It's up to them. Being satisfied with something doesn't make it correct or perfect. What's wrong with discussing the strengths and weaknesses of a technique or methodolgy. Then we can use our own minds and maybe create something even better.

    And if you disagree with the analysis - prove it wrong. Let's have a lively discussion!
     
  19. Stephen Benskin

    Stephen Benskin Member

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    If this is something he's found, great. He should show the data. He needs to prove it.

    Discussing Barnbaum's book is what I'm talking about. I believe that's the kind of thing that leads to healthy and profitable discussions.

    [/QUOTE]Regarding asking why, I think as long as we don't get too bogged down in levels of precision unattainable outside the lab, the discussion can definitely be interesting. Knowledge is a good thing.[/QUOTE]

    I agree, but asking why leads to informed discissions. Also, without questioning, how can you determine where the that level of unobtainable precision is? As my understanding of the exposure has grown, it has given me more freedom not less. It helps me understand the limitations and variances of a system or what is capable in practice and what is not. What is really a factor to watch out for and what is not.
     
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  20. michael_r

    michael_r Subscriber

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    Bond does show some curves/data in the article to support what he's saying regarding contrast with long exposures. Are they accurate? I don't know.
     
  21. Bill Burk

    Bill Burk Subscriber

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    Here's a point of criticism on the diagrams.

    OK it's just a typo but it's obvious the caption doesn't match the diagram.

    What it should say is...

    II B Reversal, Pictorial.

    H-bar is found from the average of two log H values, one
    at 0.2 above base + fog, the other at 2.0 above base +
    fog or at the point of tangency...
     
  22. Stephen Benskin

    Stephen Benskin Member

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    He does discuss film contrast, but doesn't present any data and those curves aren't film curves. They are exposure needed vs exposure indicated curves. I'm not questioning his findings (there's not enough information available to question even if I wanted), but film curves would have been nice. I know there's a real possibility that modern emulsion making has been able to reduced the effects of reciprocity. I was recently shown the Fuji Acros 100 data sheet. I didn't think it possible, but it said that the film didn't require exposure compensation up to a 120 second exposure.
     
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  23. michael_r

    michael_r Subscriber

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    You're right - sorry I was remembering the graphs incorrectly.

    Re Acros, I ran my own tests on it and found the claim to be pretty accurate. It is a pretty unique film in that respect - but its characteristic curve is also unique compared to its Kodak and Ilford equivalents. Not necessarily good or bad, but quite different in areas of high exposure. These characteristics may either have been purposely designed into the film, or they might be a by-product of its reciprocity characteristics. Not sure.
     
  24. CPorter

    CPorter Member

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    Blindly following?

    Stephen, with all due respect :smile:, your arrogance is a bit too much sometimes. So keep pursuing another method of testing, and then another, and then another,..............until all possible outcomes have been analyzed and all possible "why" answers have been found, followed by some conclusion that may illuminate some awe inspiring point of minutia. No thank you. The ZS testing I do, contacted wedge and all :tongue:, has proven quite valuable. Equating that with 'blindly following', I find, to be distasteful, but so be it. In this hobby, I accept things at face value, it should cease to be something that "works" before I spend time and money finding another way, so far that has yet to happen.
     
  25. Stephen Benskin

    Stephen Benskin Member

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    I wasn't talking about you. Really Chuck, I wish you'd limit the discussion to the facts and not always resort to personal attacks. Ad hominem attacks have no place here.

    Argue the facts. What fact have I said that you disagree with? Anything from the film speed/exposure meter relationship thread? Anything from the Hiding in plain sight thread? Anything from Comparison of Reflectance from 18% and 12% Zone Models thread?
     
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  26. Bill Burk

    Bill Burk Subscriber

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    I was suggesting Zone III is as good a place as any to look for signs of consistent density.

    I think it has something to do with it being practical (that's the kind of density you would be dealing with pictorially), plus it puts you on the straight line, so you may be able to extrapolate "close" results better than if you were on the toe.

    Interestingly Todd-Zakia discuss using a density of 2.5 which I think is absurd. But then they give an example chart with the full family of densities, 0.2,, 0.4, 0.7, 1.0, 1.5, 2.0, and 2.5 plotted to 10,000 seconds.