Why is Zone System EI often about half rated ISO/ASA?

Discussion in 'Exposure Discussion' started by Bill Burk, Mar 9, 2013.

  1. Bill Burk

    Bill Burk Subscriber

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    Zone System film speed testers often conclude that a given film's EI is approximately half (or maybe 2/3 stop below) rated ISO/ASA speed.

    Is there a simple reason? Does the fact tests are usually done in-camera, make it difficult to separate the variables and identify the discrepancy?
     
  2. ic-racer

    ic-racer Member

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    Steve had a thread on safety factors awhile back.
     
  3. Michael R 1974

    Michael R 1974 Subscriber

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    Bill, I think there are a few reasons. See my latest post in the ISO thread. This is what I ultimately wanted to get at in that thread.
     
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  4. Ian Grant

    Ian Grant Subscriber

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    Why did Kodak recommend that their 50 EI film Tmax 100 be used at 50 EI if you wanted good shadow detail and fuller tonal scale, it's there in Kodak's first datasheets. Oh and Kodak had the ASA part of the ISO test ammended before they could release Tmax 100 with a 100 ISO.

    It's about getting the best tonal range from a film, Tmax at half the box speed and suprisinglt EFKE 25 was twice the box speed - which was the Tungsten speed not daylight.

    Reality it's about what you want in your prints (or scans) if the shadow detail isn't there you can't tweak it out later. Developers make a big difference using Pyrocat HD I get almost full box speed and a long tonal scale and plenty of shadow detail.

    Ian
     
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  5. henry finley

    henry finley Member

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    Somewhere back in the early 80's Kodak did something that made underexposure and underdevelopment the new normal. I never understood it. It seems to be that way to this day.
     
  6. Bill Burk

    Bill Burk Subscriber

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    Ah, but you touched on one of about 30 topics that I am anxious to figure out... I'll keep following your thread and add where I can...

    For cross-reference...

    Post 72 of this thread...

    ISO Speed Determination Constants
     
  7. Bill Burk

    Bill Burk Subscriber

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    I like to keep in mind Ansel Adams developed the Zone System before the print studies were done. He had no knowledge of the 0.3 Gradient.

    He also aimed to correlate prints to the Weston Meter. Thus he arbitrarily labeled 10 Zones (8 if you only count the "Textured" Zones) instead of using scientifically more accurate 7 2/3 Stops.
     
  8. Stephen Benskin

    Stephen Benskin Member

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    Two reasons. When the Zone System was developed, the ASA was one stop slower that it is today. The Zone System's EIs and ASA was the same. Although the reasoning was very different. When the ASA film speed changed in 1960, the ZS didn't. Now the difference in reasoning comes into play. The fractional gradient speed was lower before 1960 because of a safety factor. The elimination of the safety factor increase film speed. The Zone System has a lower EI because it uses a different exposure meter reading to film speed ratio than the ISO standard. It is larger. The difference between the metered exposure point and the ISO speed point is 1.0 log-H (3 1/3 stops). The Zone System uses 1.2 log-H or 4 stops. While the average shadow exposure is considered to fall 1.30 log-H (4 1/3) stops below the metered exposure point, flare and the exposure constant move the shadow exposure slightly to the right of 0.10 over Fb+f fixed density.

    Speed Point - Standard Model.jpg Speed Point - Metered Exposure Ratio - Zone System.jpg
     
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  9. pentaxuser

    pentaxuser Subscriber

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    If half box speed held good for all or nearly all films when in users' hands as opposed to the strict test under lab conditions for "true box" or is that "foot speed" then wouldn't it be in film makers interests to say that while true speed is say 400 they advise users to try 320/200 as that is the speed at which film X gives proper/full shadow detail.

    Sounds like a bit of "Devil's Advocate" on my part but in reality I'd rather have instructions that rendered sufficient shadow detail at a lower speed than a "faster" film that sacrificed it.

    Of course this gums up the works for all the automatic cameras that can only read the DX code and can't be overridden and maybe for the vast majority of users, speed is better than good shadow detail.

    I wonder how many here rate their films at 2/3rds to 1/2 of box speed? If enough of we 45,000 APUGers responded under a poll of the say the three top films from each manufacturer this might give newcomers to analogue useful information.

    If 44,900 rate say TMax at 400 but only 1000 rate D400 at 400 or vice versa for balance :D then that might say a lot about the respective film speeds

    pentaxuser
     
  10. Stephen Benskin

    Stephen Benskin Member

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    Personally, I don't care how anyone rates their film. That is a question of personal taste. What the question should be is about the accuracy of a testing method and the precision of the resulting information. Technically, the Zone System can't be considered a film speed methodology. And what Bill is asking about is why it produces different test results than the ISO speed standard.
     
  11. pentaxuser

    pentaxuser Subscriber

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    Just a thought on my part which depending on the volume of pollers might produce useful information - for some. It might be useful to some newcomers to film. You are not in that category and nor is Bill Burk but just a bit of thinking "out of the box" on my part

    However I'll get back into my box now and try not to darken this thread's door again :D

    pentaxuser
     
  12. henry finley

    henry finley Member

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    What I'm curious to know after all this technical talk is said and done, is: what is the speed to set my Luna-Pro to with Tmax 100 and D-76?
     
  13. Bill Burk

    Bill Burk Subscriber

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    Hey pentaxuser,

    The box speed is great for people who use it as-is... and people who push their film to shoot in dingy dives can double or quadruple it if they like...

    Box speed is also useful for many, many purposes, because it is founded on results.

    But Zone System is a system. A System intended to get a certain kind of negative for printmaking using certain metering techniques.

    If you're not going to use Zone System, you can use ASA/ISO speed as-is and get good results most of the time. But soon as you change some part of your metering technique away from the average, you may need to recalibrate.

    Say you do something as simple as pointing your camera down to avoid getting too much sky in your meter readings. Now you messed with the average and a "different" speed would apply to your practice.

    So it's OK for Zone System speeds to be lower, while the rated speed stays what it is.
     
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  15. Bill Burk

    Bill Burk Subscriber

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    Oh, and the reason I care about the difference is that I use a sensitometer to speed rate my film.

    Then I use Zone System metering technique.

    So I want to know the difference, if it is a whole stop or two thirds of a stop. Or if the difference "depends" on the chosen gradient (I use Contrast Index).
     
  16. Alex Muir

    Alex Muir Member

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    I have 'tested' film speed for zone system purposes in various ways over the past 15 years. Most recently I have been using a Tobias densitometer. I have found the same pattern of EI being 2/3-1stop below published speed. I don't stick to one film, but I now have a set of EIs which I apply to certain films, regardless of the camera/lens/meter involved. I can't answer why this discrepancy occurs, but I have been persuaded by my test results that lower EIs produce a higher number of useful negatives. Alex
     
  17. henry finley

    henry finley Member

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    I've been loosely following this discussion front the point of view of one with a lesser knowledge of logarithms and all that other talk. And now I am dismayed at how film speeds can be all over the place, to hear you guys. Why would your zone system results be any different with the exhaustive and meticulous testing at EKC? Something is not making sense. Without going back to read every post in this thread, I don't even know what specific developer or dilution you guys are using. Still and all--2/3 of a stop slower than EKC box speeds? Something is not making sense to me.
     
  18. Michael R 1974

    Michael R 1974 Subscriber

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    Stephen - this is very important and relates to some of my recent questions in the ISO thread. Is it worth starting a thread specifically on the intervals "below metered" for ISO and ZS? Or should we discuss it in the ISO thread? Just want to make sure things don't end up too disorganized. I can PM you if it makes more sense. Don't want to sidetrack Bill's thread.

    Thanks, Michael
     
  19. AndreasT

    AndreasT Member

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    Please don't PM, just so that others can read with.
     
  20. Stephen Benskin

    Stephen Benskin Member

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    Sorry, that's not how I meant it.
     
  21. Stephen Benskin

    Stephen Benskin Member

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    Sure. Although I really got into this in the thread What is the Relationship Between Film Speed and Camera Exposure.
     
  22. MattKing

    MattKing Subscriber

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    It would surprise me if the ISO standard speed was the same as the EI used by ZS practitioners.

    Because I think that the vast majority of photographs are taken by people who would most likely choose prints that are different then the prints preferred by most ZS practitioners.

    Most people prefer lighter prints with more contrast. People who like "fine" prints tend to have different tastes.
     
  23. markbarendt

    markbarendt Subscriber

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    What amazes me is that ZS shooters don't dial in an EI that actually gives them a direct camera reading from their shadow peg.

    It is after all just a reference point.
     
  24. Bill Burk

    Bill Burk Subscriber

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    As Michael R 1974 says, these are important.

    ISO

    -Difference between the metered exposure point and the ISO speed point is 1.0 log-H (3 1/3 stops)

    ZS

    -Difference between the metered exposure point and the Zone I is 1.2 log-H (4 stops)
    -or-
    -Shadows are commonly placed on Zone II which is 0.9 log-H (3) stops below the metered exposure point

    ---
    ISO
    -Average shadow exposure is considered to fall 1.30 log-H (4 1/3) stops below the metered exposure point

    ZS
    -Zone I is considered to fall 1.2 log-H (4) stops below the metered exposure point

    ---
    ISO
    -Flare is about 0.4 log-H (1 1/3) stops to the right.

    -Exposure constant is ... ?

    ZS
    -Flare is embedded in the tests?

    -Exposure constant ... is this ignored?
     
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  25. Stephen Benskin

    Stephen Benskin Member

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    The exposure constant is the numerator in the film speed equation. While the speed point is chosen because of it's relevance, it might be desirable to place the exposure at a different place. Any number other than one actually determines a point other than the speed point for the exposure placement. What if the ISO speed equation was 0.4 / Hm? This would offset the exposure by a stop.

    BTW, I don't see the ZS EI as being designed for the discriminating taste of the photographic elite. It's just the safety factor from before 1960. All anyone has to do is take the ISO film speed and cut it in half.
     
  26. Bill Burk

    Bill Burk Subscriber

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    That's a short-circuit (which I occasionally do) by taking the usual outcome without stepping through how to get there...

    Steps for testing for Zone System film speed are well (and inconsistently) documented... There isn't any intention to include a safety factor. Its a specification of quality that shadow detail is required.

    And it may not correlate to the first excellent print criterion, the negative that fits Grade 2 under Zone System, may well be exposed a stop above the "first excellent" print.