Exposure

Discussion in 'Black and White' started by brizzybunny, Oct 8, 2020.

  1. And where is that "O" mark?
    Only three stops above Zone V, that's where!

    I can see that words alone aren't going to convince.

    Here's a Kodak calibrated greyscale against an evenly-lit surface that I'd definitely call "Whites with texture and delicate values...". The definition of Zone VIII according to Adams (p. 60 of 'The Negative' - 6th printing 1984).

    Exposure was ISO 400, 1/13th s @ f/2.8, according to an incident meter reading from centre frame.
    13th-sec.jpg

    Now the same, at the exposure indicated by a spot reading from the whitewashed wall above the greyscale. I.e. placing the wall on Zone V.
    50th-sec.jpg
    This clearly shows the subtle texture in the paint (crazing and brush strokes).

    Here's the same with exposure compensation of + 2.33 stops applied to the camera - i.e. placing the white wall at Zone VII + 1/3rd.
    10th-sec.jpg
    The camera indicated a shutter speed of 1/10th sec.
    I've also superimposed part of the greyscale from the 'Zone V' exposure to prove that there is a genuine 2.33 stops difference between the exposures.

    Each division on the Kodak greyscale is a density step of 0.1, which equates to a 1/3rd stop exposure step. So step 7 = 2.33 stops.

    Now let's try to place the wall on Adams' Zone VIII with a + 3 stop compensation.
    8th-sec.jpg
    Whoa!
    Where have all our "texture and delicate values" gone?
    Blown out, that's where.
    So much for 3 whole stops between Zone V (=18% reflectance) and Adams' description of Zone VIII, plus his insistence that each Zone is exactly a stop change in exposure.

    This is easier to see in a histogram, where the white wall endstops the right-hand side of the graph.

    OK. It's only half-a-stop, and you could get away with that in B&W film. Not so with a digital JPEG, where that extra third to half a stop exposure is critical, and will blow away that delicate detail needed in near-whites.

    So, if the Zone system is to stay relevant in this digital age, then its Zones need re-defining.
    Or we can simply work in good 'ol f-stops and chuck the pretentious Roman numerals away for good. Since adding the Latin for one-third or one-half a Zone would make an over-complicated system even more unwieldy.

    FWIW. The 'M' step (0.7D) on Kodak's greyscale above actually represents a reflectance of close to 20%. A true 18% reflectance would have a density of 0.745. So there's a discrepancy of about 1/7th of a stop. The camera also only indicates exposure times to the nearest 1/3rd stop, even if the exposure time is given more precisely - if those things worry anyone.
     
    Last edited: Nov 29, 2020
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  2. It still is worth pointing out, i see, that Zones are what you want how parts of the scene in front of you appear in print.
    Measure an x stop difference in subject brightness, apply compression (usually) or expansion as necessary to get what you 'previsualised', and that x stop difference is not an x zone difference. That is, unless you want it to be.
    Zones are described in terms of what printing paper can render, and how it does that. Not in terms of subject luminance differences. The Zone System is about bending the latter to match the former, in a controlled way. The result of that control over differences in stops are Zones. Zones are not stops.

    Can we use zones when the output medium no longer is an emulsion on paper? Of course we can. And then still zones are not stops. Zones are how we control the apperance of dark and light bits and everything in between. How we tame those blinking bits on our editor screens. Not the measured luminance values of the parts in the scene that lead to those blinking bits.
     
  3. James G. Dainis

    James G. Dainis Moderator

    To re-quote Ansel Adams - "We define a one stop exposure change as a change of one zone on the exposure scale, "

    Zone 7 is a two stop exposure change over zone 5. If one wants to expand a difference after the exposure has been captured, then one give increased development to move that zone 7 to zone 8.

    I think people are arguing over printed zones rather than exposure capture zones. The zone system starts with the exposure capture. (a one stop exposure change as a change of one zone on the exposure scale,) Modifications in development and printing come later.
     
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  4. That's not quite correct: modifications start at the previsualisation stage. The target is the Zone, in print. The aim of the exercise is to measure and modify such that whatever difference in exposure values there may be, these differences end up as the difference (and placement) in zones that we are after.

    Yes, you start with differences in exposure values, in stops, that on an ideal film and ditto paper (i.e. straight line, no shoulder and such) also are rendered as one stop differences. Then stops (both in the scene and at the print stage) and zones are identical. In real life all film compresses the differences, and unevenly too. And those compressed differences are expanded again (though not as much), unevenly again, when printing. A one-on-one relation between stops in the scene and zones in the print is impossible to achieve, and rarely wanted.
     
    Last edited: Nov 30, 2020
  5. The descriptions of the exposure zones are still being conflated with those of the print values, it seems to me.

    The descriptions are essentially the same up until about Zone VI, but because the brighter tones (exposure values greater than ~7.5) must be compressed to make them fit onto the paper's tonal scale, the descriptions deviate for Zones VII and up. Thus, Zone VII (paper white in the scene) is described as "light gray" in the print, and Zone VIII (semi-specular reflections) as white "with texture and delicate values" in the print. (Compression also applies to the darker tones, but for some reason the dark tones are not being disputed in this thread.)

    It can be readily seen, in rodeo_joe's correctly exposed example, how Patches 1 and A (Exposure Zones 7 and 7.3) are displayed as light grays compared to PNet's white background.

    Adams could have chosen to just simply truncate the tonal scale at a zone value of 7.5, like was done with the digital scale, but he designed the model to include semi-specular reflections (VIII), specular reflections (IX), and light sources within the image (X).
     
  6. I cannot believe I'm writing this with my poor english... please be indulgent! :D
    A definition is "something, typically expressed in words, that attaches a meaning to a word or group of words... " (Wikipedia). So IMHO, the aim of Adams` definition is not to make an obvious scientific statement, but to make an inseparable relationship between two facts, the metering (range) of a scene and the way this scene "should" look on the printing paper.

    I see some abstraction in Adams` definition: "We define a one stop exposure change as a change of one zone on the exposure scale, and the resulting gray in the print is considered one value higher or lower on the print", we cannot take some words apart just because all are part of the definition.

    Let`s analyze Adams`words:
    -We define a one stop exposure change,.. he is giving the basis or starting point of his idea, the action of subject measuriement.
    -... as a change of one zone on the exposure scale,... looks pretty obvious, but may be not... as explained in the post #119, one mark in the meter is not related to the measuring (although it could seem obvious) but to the idea of print density (the abstraction). In the same way we cannot explain historical facts from a current point of view, to know how they used to work could help to understand the real sense of his statement. Cannot remember if it was Adams or another who used to literally stick some gray shades on the meter for that reason. I think many people have their meters this way, and some print homemade dials as well.
    -... and the resulting gray in the print... so there is a conjunctive fact/result direct relationship or correspondence between that exposure scale mark and the print density.
    -... is considered one value higher or lower on the print. to clarify the idea of working in full steps (not f stops), which will be called "values", and will be the equivalent to that stops on the (real) scene.

    Agree, in a "normal" range scene, three stops above the Zone V doesn't match the print Zone description (please notice that I use that "abstraction", I mix the purely objective meter data with the somewhat subjective "Zone value" idea) The question is, should it?
    So I personally think that the definition is one way only, it cannot be taken in the opposite direction. One Zone value separation on the print don't necessarily have to be one f stop difference in the scene. And if so, it'd be contrary to the aim of the method, so it wouldn`t make sense.
     
    Last edited: Dec 1, 2020
  7. Agree, it may be that the (film) Zones description needs to be adapted to other materials ... for example, if you can get much more shadow detail using a digital camera with the same exposure, the game changes... It will depend on the usable latitude range of each material.
    But I wonder if it'd be practical anymore... to me, the charm of the Zone System is attached to film, specially on a LF camera.
    On digital, the histogram is the only thing I need. Maybe any kind of custom adjustment on it could be perfect.
     
    Last edited: Dec 1, 2020
  8. If anyone still interested, looks like St. Ansel wrote his own answer in the introduction of "The Print" (1982). I read:
    "... I wish to dispel here any thought that my approach is rigid and inflexible. I cannot repeat this too often! I have found that many students read descriptions of procedures in a rather strict way, and are then consumed with the effort to produce exact relationships between subject luminance values, densities and print values. No matter what he does the photographer cannot violate the principles of densitometry, but densitometry is a tough discipline and will tolerate a good amount of bending without breaking!"
     
  9. Then why the f... did he make such a song and dance act out of it?!

    Come on; hands up. Who actually exposes individual sheets of film, and then proceeds to give them tailored normal, curtailed or extended development?

    .... anybody?

    The very popularity of rollfilm, 35mm, remote processing labs, and especially reversal/transparency material show how widespread true use of the Zone system wasn't and isn't.

    Because colour reversal material is totally unforgiving of exposure changes, and thinking that it's capable of capturing 9 one stop separated Zones is a recipe for complete failure and disappointment.
    Likewise with straight OOC digital Jpegs. No gently rolling-over H&D curve there to cover up a misjudged brightness differential.

    Yet RAW digital files now give us the chance for a renaissance of the Zone system's principles - with post-processing 'development' tailored to individual exposures.

    In fact not just the slope of the tone curve, but its entire shape is open to manipulation. Of which, I'm sure, Adams would have approved.

    Just as long as we don't delude ourselves that we can capture brightness values up to 4 stops higher than an 18% reflectance, while simultaneously placing that 18% reflectance at mid-grey. Limit your 'whites' to 2.5 or two and two-thirds stops above a nominal Zone V and everything will be fine.

    I'm not going to propose a fully-formed alternative 'zone' system for the digital age. Maybe 'Expose To The Right' is all that's needed. Or some slight expansion on that.

    But I will propose that Adams original Zone system no longer has much relevance today, in the form he published it, over half a century ago.
     
    Last edited: Dec 4, 2020
  10. The zone system is to allow you to visualize the final image even before you make the exposure but today with digital you don't need that.
     
  11. James G. Dainis

    James G. Dainis Moderator

    "Come on; hands up. Who actually exposes individual sheets of film, and then proceeds to give them tailored normal, curtailed or extended development?"

    I used to do that all the time when shooting 8x10 or 4x5 film. On a bright sunny day I may have had to use N-1 to lower the highlights to Zone 9 and on darker cloudy day N+1 would raise the highlights up to Zone 9. But you are right, I no longer do that. I haven't shot film in a long time.
     
  12. You need that with digital too. Maybe not so much for technical reasons. But if you do not have an idea of what picture you are creating the moment you press the button, maybe it would be time to put the camera down and pursue some other thing.
    Decisions about what to do to get that what you want still have to be made. We still have to intervene to get there. And still have to consider the limitations of the medium and how to bend things to get where we want to be.

    And that's what Adams said when he explained the zone system: it's a way to bend things so they end up fitting in our prevision.
    And that's what he did to the zone system: bend, cheat, whenever it was necessary to do so.

    Is the zone system practical? Sure it is. To begin, it was and still is a very good teaching tool. Then, it has to be remembered that it is 'just' a formalized expression of the age old truism "expose for the shadows, develop for the highlights". Which is still true now we're using digital capture ("expose to the right"). Further more, it gives more control over the process than the truism (which says nothing about how to do that), and can be used in a very practical way (unless you're a miniature format photographer who habitually captures two consecutive christmasses on one roll). You need two magazines, and an empty spare for when you can't get what you want using the film in the other two, designated to whatever n+ or n- variation you thought you would need. Remember: previsualisation. You rarely went out for a shoot on a sunlit beach with ISO 1600 film, or for a dim jungle shoot with ISO 32 film. We know in advance what we most likely need when we go out.
    So yes: very practical.

    And please stop that talk about precise and correct reflectance values and such. It has been said often enough that that is misguided, missing the point of the zone system.
     
    Last edited: Dec 4, 2020
  13. Then why do most Zone system enthusiasts put such store on 'calibration' and poke a spotmeter at every part of the subject?

    And are you arguing that there is no value in knowing exactly where 'white with texture' will fall in the final image for a given exposure?

    Let's just stick a wet finger in the air to get an exposure reading then, shall we?
     
    Last edited: Dec 4, 2020
  14. Why? Because you have to. To know 'where you're at' and what to do next.
    That's not the same as harping on about differences in stops and 18%.

    I am most certainly not arguing that. If you think so, you show you do not get it still.

    You mention calibration as part of the zone thing. Think about that.
     
  15. It should probably be pointed out that the Q-13 grayscale photos posted above have captured only a 5-stop range from a scale that spans a known 6.3 stops. Should one conclude that this is somehow considered good or that digital is a complete failure and disappointment?
     
  16. It should be realised that most of that shadow compression is due to the limitation of an 8 bit JPEG and the non-linearity of the sRGB tone curve.

    You could take a picture on any medium you chose, and it would still look much the same after being mangled by JPEG compression and most displays' colour-space.

    Plus there isn't a camera and lens yet made that doesn't add some shadow flare through glass surface and dark-chamber reflections. Such that you can never get an exact one-to-one tone-curve relationship between the real world and the image plane. Especially at low brightness values.

    In fact, the old and poorly-coated glassware used by Ansel Adams may account for some of the highlight compression and discrepancy between his real-world brightness values and captured Zones.
    Sorry, but it is exactly the same as 'harping on' about differences in stops.

    Poking about with a spotmeter will only confirm that there are no more than 2.5 stops difference between a grey-card reading and a matt white surface. Whether that's a whitewashed wall, a fluffy white cloud, or freshly fallen powder snow.
     
    Last edited: Dec 8, 2020
  17. It seems you are saying that digital is inferior to film.

    However, the flattened tones shown on that Q-13 scale are fully 3 stops lighter than the area where JPEG/sRGB data problems begin to occur. My not-very-special monitor will readily display another stop below that from JPEGs, so in my view the rather obvious problem lies somewhere other than the file format.

    Curiously, I have a cheap old JPEG-only Canon CCD point and shoot with a super-zoom lens that will easily reproduce every step on that scale.

    I'm not privy to Adams's lens selections, but I am guessing that if wanted to capture all 11 zones, he was not probably not using his worst lenses.
     
  18. Although I think the 1 stop = 1 Zone description issue mentioned here is irrelevant to the practice of the Zone System, there must be an original reason to use that "definition" ... Personally I consider it is plenty clear, but I understand that could not be "the clearest". We know there are different opinions (and reasons) about that.
    I think to know the real answer we should have a deep knowledge of Adams` very personal procedures and results (that I don`t have), probably beyond what is written on the "trilogy" (or "tetralogy")... We are translating an objective metering of the scene into relative contrast values on paper, an outdoor scenario with variations in brightness to printing materials that could be quite different from one brand to another... it is a complete process developed many decades ago that cannot be analyzed disjointedly or uncontextually without falling into somekind of "legal fraud".
     
    Last edited: Dec 11, 2020
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  19. I learned photography with digital first, and I think it’s the best way to go. As someone else said, it’s instant feedback, not instant gratification. It allows the student to receive constructive criticism at a reasonable time. Plus, it’s exciting, seeing a well made shot in real time. I think it gives you more incentive to stick with photography. Once you master the basics, and get to the intermediate level, then start shooting film.
     
  20. Vincent Peri

    Vincent Peri Metairie, LA

    Hi Rodeo Joe.

    I read with great interest your point about zone VIII being an impossible 144% reflectance. I was reading about the same point on a Photrio forum about the same topic.

    Someone there posted this quote about a previous poster saying zone VIII should have no texture at all:

    "I think you are conflating reflectance with exposure value. Each step is not doubling reflectance but relative brightness which can go up or down without a limit."

    The quote is from post #21 on this thread: Zone system mathematically inconsistent

    That sounds reasonable to me, but I'd like to get comments on it.

    Thanks.
     
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