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  1. #11
    Bill Burk's Avatar
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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.

  2. #12
    Bill Burk's Avatar
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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).

  3. #13

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

    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

  4. #14

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    Quote Originally Posted by Stephen Benskin View Post
    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.

    Attachment 65480 Attachment 65481
    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

  5. #15
    AndreasT's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    Stephen - I can PM you if it makes more sense. Don't want to sidetrack Bill's thread.

    Thanks, Michael
    Please don't PM, just so that others can read with.

  6. #16
    Stephen Benskin's Avatar
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    Quote Originally Posted by pentaxuser View Post
    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
    Sorry, that's not how I meant it.

  7. #17
    Stephen Benskin's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    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.
    Sure. Although I really got into this in the thread What is the Relationship Between Film Speed and Camera Exposure.

  8. #18
    MattKing's Avatar
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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.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  9. #19
    markbarendt's Avatar
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    Quote Originally Posted by MattKing View Post
    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.
    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.
    Mark Barendt, Ignacio, CO

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

  10. #20
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    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 ... to the right ...
    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?
    Last edited by Bill Burk; 03-09-2013 at 09:48 PM. Click to view previous post history. Reason: corrected

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