Exposure

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

  1. Leaf shutter or focal plane shutter?
     
  2. Yes, it precisely does. Because that's exactly what Adams states.

    If you want to rewrite Adams trilogy of books - fine. Go ahead, but don't expect many sales.

    Look, if you don't have a fixed exposure spacing (or at least a well-defined set of spacings) how can you possibly arrive at an exposure that places the tones where you want, relative to each other?

    Your only control over Zone spacing in the print is to change the contrast (gamma) of the negative during development. If you also change the Zones' exposure relationship, then you have no baseline to work from in order to vary that contrast. Nor any sensible way to place the tones where you want them. It becomes a system with unstable feedback that just becomes chaotic.

    In short, you might as well wish for Zone 3 to appear lighter than Zone 7 by describing the Zone differences as minus one stop. Ridiculous? Yes, but no more ridiculous than having flexible Zone spacings at the exposure stage.
     
    Last edited: Oct 28, 2020
  3. You can repeat it as often as you like, but you're just contradicting what Adams clearly stated, and your own previous assertion....
    With no fixed brightness spacing between Zones, how can you decide on an exposure and development time?

    Say you meter a tone that you want to place on Zone 5. You then meter something that's two stops brighter, but want it placed on Zone 9. That tells you that you need to overdevelop by N+2. But you can only decide that by knowing that each Zone is (by default) one stop apart. If the Zones were two stops apart to begin with, then you would only need N development.

    See? You need fixed points of reference to begin with. And if those fixed reference points aren't quite right, then the whole system starts to fall apart.
     
    Last edited: Oct 28, 2020
  4. Yes, that is indeed the general idea. We decide in what zones parts of the scene must end up in (within the limited possibilities), and adjust exposure and processing such that a given, metered luminance difference ends up as our desired zone difference.
    Zones are not EV values or such. They are part of our previsualisation. They are what we want the print to look like. Zone 0 is black, no detail. Zone V is a middle grey between black and featureless white. What EV values or how many stops apart in the scene they may be determines how we must expose and develop. But the zones are what we assign those luminance values/differences to. They are not luminance values (you can make a full range print - all zones - from high and low light scenes alike). Nor is the difference between zones a fixed difference in luminance values.

    That is the entire point of the zone thing: we take control. We do not let a scene dictate how it will look like in our rendition of it. Who cares that the difference in luminance between a black cat and white snow is so many stops. We want them both to look grey, so we make it happen. (A bit too ambitious, since there are limits to what we can do, selecting film, exposure development, print grade, paper developing, etc.)
    We have to know how many stops difference there is, yes. And we have to know what film to pick, how to expose and how to process and proceed beyond that. But knowing EV values does not make zones have a fixed value.
    You say that each zone is one stop apart. Maybe, if you do expose for middle grey and do nothing special, and use a straight forward, long straight curve film with no toe and no shoulder. Vary ythose parameters a bit, and zones no longer are one stop apart. have a film with distinct toes and shoulders, and even with straight processing but adjusted exposure, the differences aren't a fixed value anymore. Et cetera.

    All not important, and way too complicated, when you use a digital camera. At least, that was you point, wasn't it? Zone system is nevertheless a great teaching tool, that helps understand exposure and what comes after that, whether it is in fluids or on a computer. Much more than looking at a screen on a camera can.
    Zone system is not very practical. It has severe limitations. But that is another matter.
     
    Last edited: Oct 28, 2020
  5. Well, you have gotten me at the semantics. I don't feel comfortable here, my english is not as good as I would like.
    Personally, the word "Zone" is always related to the print, or what is the same, to the grey shaded scale that are the Zones, from 0 to X. It is always the print.
    When I'm at the scene, I think (visualize) the scene in terms of Zones. So when I said
    I`m obviously saying that the stops belong to the scene metering and not to the Zones or description of Zones. There is obviously a relationship, but not closed or precise, this is the important thing.

    After reading your posts I assume there must be an Adams phrase that states what you say (don't have the book here), but even if so, Ctein`s words came into debate... the one-stop-equal-to-one-Zone is "by definition", it must be taken with a pinch of salt.
    And, what if so? It doesn't change Adams` Zone system. The method is perfectly feasible, being -or not- one zone=one stop (step of gray shade/exposure, I mean).

    I think Adams had a printed grey scale attached to his own meter (Weston?), or he recommended to have it this way. So I assume the aim was (very likely) to visualize the values with an easy, practical method. But think on it... does it makes sense for any other reason? And again, what if the meter, instead of reading 18% reflectance is actually reading 12%? And the most important, does it change the sense or the usefulness of the Zone System?
     
    Last edited: Oct 28, 2020
  6. Yes, of course you are right here. Tests must be done to get the tones or values, with precise spacings, one stop exposure differences to get each Zone.
    This is actually the closest relationship between the Zones and the one stop exposure in the scene; but think that all the tests must be done under controlled conditions and with the same grey card (towel or whatever), where the real scene is quite variable, so the "Definition of Zones" cannot be taken as a precise metering reference.
     
  7. "Description of zones" (table of), I mean.
     
  8. Yes they are!
    At the metering stage the Zones are - according to Adams - precisely one stop different in brightness value. This is completely divorced and separate from how you make them appear in the print.

    Exposure measurement is one thing. Translating that to a print is a completely different part of the process.

    Even though you might envision the end result before you even meter it, there is a sequence of steps to be gone through, and one of those steps presumes that your metered Zones are one stop apart. How you expose and develop those brightness values then determines the print Zones, which are not the same thing at all.

    Let's get rid of Zones for a while and put it on an objective and scientific basis.

    You meter a certain area (A) in a scene, that after passing through the lens aperture throws 0.1 lux onto the film surface. There is another area (B) of the scene that throws 0.2 lux onto the film surface, a 3rd area (C) that illuminates the film with 0.8 lux. Those areas (A) and (B) are 1 stop apart, while areas (B) and (C) are 2 stops apart. Short of adding extra light to, or shading an area, there's absolutely nothing you can do to change those brightness relationships. They are what they are, and all you can do is to measure them. And it's only after measuring them that you can decide how to process the film such that you get a suitable density difference between those areas. A density difference that when printed will give the desired density difference(s) in the print.

    Of course the light meter works out for you the shutter speed needed to get those lux values at the right part of the film curve, and a chart or experience can then help you decide how to develop the film, but, I repeat, there is nothing you can do at the point of exposure to alter the brightness relationships between parts of the scene.

    All you can do is measure those brightness values.

    When put in those objective terms the procedure isn't easy to grasp. So what Adams was trying to do was to generally categorise some of those fixed subject brightness relationships and make them easier to visualise as print tones.

    And all I'm arguing is that he categorised some of them unrealistically. Such that the claimed brightness differences aren't physically possible.
     
    Last edited: Oct 29, 2020
  9. That's the whole point.
    It's Adams stance that his (scene) Zone definitions do fall at precise one stop intervals.

    While I claim that his definitions of Zone V and Zone VIII absolutely preclude a 3 stop difference between them.
     
    Last edited: Oct 29, 2020
  10. Let's take a practical situation:

    There is a given scene, e.g. a close portrait on a badly lit scene. Check the sketch below.

    sketch.jpg

    You start the metering process, and you get the readings as follow: Background at left, 3 EV, face 4 EV, background top at right 6 EV.
    The scene is low in contrast, but you want to get the best printable negative.
    You want to place the background on the Zone III (quite normal); so the face will fall in zone IV (still too dark), and the back brightest area in the Zone VI.
    It is, one stop difference from Zone III to IV, and two stops difference between IV and VI. Right?

    So we plan to proceed. According with Adams` Description of Zones,
    -Zone III is right as a background, we want to start it dark but with a little texture. As Adams` description.
    -Zone IV is definitely too dark for my taste, I'd like it at least on Zone V. Adams say caucasian faces are Zone VI.
    -Zone VI is still too dark for a highlight, I want it in Zone VIII, as Adams say.
    So separation is of eight steps or Zones, I`ll check my testing charts and I'll expose and process the film accordingly.

    What does your argument say in this case?

    Well, I haven`t measured the difference between a dark face (how dark?) and at fallen snow (damp or cold?), but I'd take it as approximate...
     
    Last edited: Oct 29, 2020
  11. As Flounder said in Animal House,
    Here I was getting nostalgic about how calm, polite, and bloodless this site had become. :rolleyes:
     
  12. In Artificial Light Photography (Book 5 of the original series) Adams provides several tables that show where Zones V and VIII fall relative to magnesium carbonate, which was his reference for the highest diffuse reflectance (96% reflectance, approx. zone 7.4). From these tables and the surrounding discussion it's pretty obvious that Adams was clear about the relationship of the exposure zones.

    Hopefully, there should be a similar passage in the three-volume rewrite.
     
  13. just get a light meter folks and worry about the scene
     
    rodeo_joe|1 likes this.
  14. That's interesting information. I must try and find a copy of that document.

    It also makes it even more strange that Adams should then proceed to describe such objects as white picket-fences, freshly fallen powder snow and suchlike as having a Zone 8 reflectance. When it's easily demonstrable and measurable that their reflectivity is close to 100% and therefore, as you say, reflect only about 2.5 stops more light than an 18% card.
    Perhaps you could expand on that? Because to me it seems to show that he disregarded any photometric evidence and went ahead to declare a faulty (but convenient) one stop interval between Zones. Or at least between Zones 5 and 8.
     
  15. Are you saying that nothing is brighter than a piece of blank white paper?

    (I believe, although I am not entirely sure, that the sticking point seems to be the description of Zone 8 as "textured white".)
     
  16. No, of course I'm not.
    Specular reflections can obviously be a lot brighter.

    What I'm taking issue with is Adams' insistence that inherently matt white objects (as per his Zone descriptions) reflect 8 times more light than an 18% grey card. They don't!

    Thinking on this has me wondering why he just didn't work in stops to begin with. They were in use long before his appropriation of them as Zones.

    How much easier to say that "matt white stuff is about 2.5 stops brighter than a grey card" and "generally you can't see any detail in shadows that are more than 4 stops darker than a grey card". This was, I'm sure, common knowledge to photographers long before Adams tried to formalise and (over) refine it. And in the process attempted to neatly categorise a haphazard world into convenient - and wrong! - pigeon-holes.
     
    Last edited: Nov 22, 2020
    murray_kelly likes this.
  17. Zones are things you can change, assign to different brightness levels. I can decide that two stops over middle will be zone vii, or viii, or even iii. We have control over this.
    Stops are stops.
    That's why Adams needed and invented Zones, and didn't just use stops.
     
    Dave Luttmann likes this.
  18. That's what I was thinking the trouble spot was: the interpretation of the words that describe how something looks. The tables and related text I previously referenced make it abundantly clear that matte objects do not fall on Exposure Zone 8 in the Normal exposure case.

    I think I vaguely remember him commenting on that somewhere, but don't remember what or where. Imagine, though, how confusing a zone progression of II.VIII, IV, V.VI, VIII, XI,...,LXIV would be! At any rate, a fixed geometric relationship could apply only to exposure zones--it would not work with negative or print zones--so some type of abstraction is necessary.

    The conceptual errors I have seen in this thread are not Adams's.
     
    Dave Luttmann likes this.
  19. As far as I know, in the early days Adams based the Zone System zones on the dial of the Weston meter that he used to use:
    westonone.jpg
    This meter consider the useful range of a normal subject in seven stops, so from textured white to textured black. The dial has eight marks, that is, seven blank areas.
    The mark on the right says "O" (overexposure) and the one on the left says "U" (underexposure).
    But for whatever reason, Adams used the marks as steps, rather than separating points. It seems that Minor White used to do the very same thing.
    So they considered eight zones instead of seven stops. It could seem unscientific, maybe, but it is his system.
    After that, he added two more zones, for black and white, without texture. Ten zones, from 0 to IX.
    I understand that the original Zone System is a symmetrical black-to-white system, "texture-based" is the goal of the method. And it is important to know that Adams executed it in a practical and very personal way.
    In "The Negative" (12th ed.), I can read on the description of Zone VIII (page 60): Whites with texture and delicate values; textured snow; highlights on Caucasian skin.
    I cannot see where it doesn`t match the aim of the system and the origin of their proposal. It`plenty clear to me that snow "should" fall as a Zone VIII on the print, whatever the distance from the middle grey the meter say it is in stops.
    Snow reflectance can vary somewhat widely, depending on several factors... even so, you may be right if we were talking about the Munsell`s scale. But we are talking about Adams Zone System...
     
    Last edited: Nov 22, 2020
    q.g._de_bakker likes this.
  20. On page 49, he says: 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.
    Still plenty clear to me. So the useful range of seven zones (or eight), still apply...

    Is actually the meter reading of a textured snow out of that range? Maybe, not sure. I think there are different types of snow, and different reflective characteristics, depending on the thickness and base. I'm a fan of backcountry skiing, so for sure I'll get the meter when the season rolls around... (Provided that the Covid and our beloved authorities allow it!!)
     

Share This Page