Zone System Zone VIII Development Test Using a Scanner and Densitometer

Discussion in 'Film and Processing' started by randy_johnson|5, Jul 17, 2017.

  1. Since many folks prefer to scan black & white negatives and print on a photo printer rather than print using an enlarger, I would like to propose a way to calibrate the Zone VIII film development test using a scanner and densitometer.

    Needed: A photo scanner & densitometer.
    (Note: it is possible that some scanners have a densitometer capability but I am not knowledgeable)
    A photographic film tablet (step wedge) – calibrated or not.
    Knowledge in how to do the Zone System film speed test.
    A photo printer

    Step 1. After completing the film speed test, then expose a negative for Zone VIII. Develop the film normally according to the manufacturers instructions.
    Step 2. Scan the photographic tablet (step wedge) and print it on your printer.
    Step 3. Choose the step that best represents a Zone VIII print value that has just a bit of tone before all other steps are pure white.
    Step 4. Measure the density of the step that prints Zone III.
    Step 5. Measure the density of your exposed Zone VIII negative and compare with the density of the step wedge in the previous step.
    If the step wedge density is greater than your exposed Zone III exposure increase development time by 25% and re-test as above.
    If the step wedge density is less than your exposed Zone VIII negative then reduce development time by 25% and re-test as above.
    I believe this system will yield Zone VIII negative values that will print as Zone VIII print values.

    If you don't have access to a densitometer you can try and eye ball the comparison between the step wedge and Zone VIII negative. It will at least get you in the "ball park."

    Thoughts?
     
  2. Using a scanner as a densitometer is an ancient idea, and one that's been given plenty of airing on P.net and elsewhere years ago.

    But which Zone VIII would you use? The one that's sensitometrically correct, or Ansel Adams' strange fudge where Zone V is only 2.5 stops less?

    Reading from AA's "The Negative":
    If a "pure white" object with an assumed Lambertian reflectance of 100% (or close to) is allocated to Zone 8 - sorry, can't be bothered with the Roman numerals anymore - and each zone has a one stop spacing; then zone 5 should have a reflectance close to 12.5%. But no! AA claims a zone 5 reflectance is "mid-gray" at 18% reflectance. One half stop higher than it logically should be, and making objects at zone 8 have a reflectance of 144%!!

    If the man that invented the system can't even be consistent in its application, then what use is that system?

    And who today is going to develop individual frames to N, N -1, or N +1 etc?

    The idea of keeping the printable and scannable Dmax to 1.8D or thereabouts is absolutely sensible. But please drop the archaic and imprecise Zone VIII when referring to it.
     
    Last edited: Jul 18, 2017
  3. It seems to me that if this is true, then nothing will be of use.
    Adams's use of the system was practical, not theoretical, in any case
     
  4. Not having actually used the zone system, but having read Adams' book about it,

    the dynamic range, the difference between minimum and maximum log reflectance, of paper is much less than the density range of film, or the range of some natural scenes.

    With a transmission densitometer, film, scanner, printer, and reflection densitometer, you should be able to set any desired mapping between film density and print reflectance. (Normally monotonic, but that might not be required.)

    The minimum reflectance is limited by specular reflection from the surface, or even worse if in a frame with glass, reflection off the glass.

    In the case of inkjet printers, I believe that the range of drop sizes isn't as big as you would like, so the printers have to dither them, print an appropriate number of the smallest drops over a gray area, to give the right average reflectance. If you don't look too closely, that should work fine.
     
  5. "Adams's use of the system was practical, not theoretical, in any case"

    Then why did he seemingly spend hours (days, weeks?) compiling his own sensitometric curves for umpteen different film/developer combinations and devote more than half of the space in his books to exposure and development theory?

    I'm not arguing with the concept of pre-visualisation, just the rather arcane (and inaccurate) system of reference used; when f-stop steps would serve the purpose more accurately and logically.

    "the dynamic range, the difference between minimum and maximum log reflectance, of paper is muchless than the density range of film,"
    - That's debatable. B&W negative film should have a density range of only around 1.8D to comfortably scan or print easily. That's a contrast range of just over 60:1, which is comparable to, or slightly less than, the reflectance range that can be achieved on Baryta-based glossy paper (about 2.1D).

    And of course the reflectance range of paper or density range of film is less than the subject brightness range encountered in the real world. That's why the translation to a transmissive or reflective medium requires the application of a gamma curve; a function that's built into the chemistry of film. Helped along by lens and camera body flare.
     
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  7. Comfortable, fine, but end to end it is more than that.

    Normal subject don't have so wide a range, but when part is in sun, and part shade, it is more.
     
  8. "Comfortable, fine, but end to end it is more than that."
    - Then it's not going to be easily printable without dodging/burning and a scan will likely lose detail in highlights.

    The point is that development should be adjusted to keep wanted highlight detail within the region of 1.8 to 2.1D. Obviously, specular highlights or included light sources may go above this, because keeping those highlights printable/scannable would result in an overall very thin and flat negative, and having such highlights print as blank white is entirely visually acceptable.

    IMO, if you're regularly getting a Dmax in B&W negatives of >2.1D you should seriously consider cutting development times, and colour negatives should definitely not have densities above that level.

    Reversal film is another matter entirely, since its exposure and processing need to follow strict protocols, and it's density range is geared to direct or projected viewing.
     

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