When is a Zone no longer a Zone?
When I began writing Death of the Zone System I never expected this minute detail to grow into a full-blown post, but I realized it was worth addressing after reading a specific statement on Martin Bailey's blog. In the past few posts I have drawn from his article on the Zone System repeatedly merely for the reason that it provided a good source of common misconceptions. Don't take my repeated exploration of this post as a condemnation of what is really a helpful and clear resource for photographers.
The comment that inspired this article is this:
"Although I’ve seen heated arguments as to whether or not a Zone is equal to one stop of EV or Exposure Value, Adams himself clearly states that this is how he intended the zones to be used.."
"Now, in practice, we’ll find that as the dynamic range that our cameras can record increases, strict use of The Zone System requires that we will have to move away from thinking of each zone as one stop of exposure, or, simply use more zones, keeping the zone to EV stop relationship."
The reason it gave me such pause is that while I find many circumstances in which each zone is a one stop change in exposure, I also find plenty of circumstances where this is not the case. Bailey recommends that now with the greater dynamic range of digital we need to expand the amount of exposure each zone contains or add more zones. I have addressed in parts III and IV the fallacy in this reasoning, but have yet to really prove how flexible the Zone System becomes once we take a more nuanced view of how the Zone scale is expanded or contracted to adjust for different subjects under a range of different contrast ratios.
So, is each Zone equal to a one stop change in exposure? At first I couldn't believe that Adams would so rigidly define each Zone as a 1 stop change in exposure, but looking back to The Negative I found that this is precisely the case (1981, 49).
"...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 scale."
However, even though I learned a great deal from the three books of the New Ansel Adams Photography Series and they are treated as critical reading for any photographer I must admit that I have found a far more comprehensive, albeit dense, explanation of ZS in Phil Davis' Beyond the Zone System. After guiding the reader through sensitometric testing and plotting of films and papers Davis gets down to brass tacks about precisely this question (1988, 139):
"Although the '1 stop equals one zone' concept is easy enough to understand and apply when we're dealing with a normal subject, it raises an obvious question when the subject range is greater or less than 7 stops. Does a 9-stop subject have a 9-zone range, and a 5-stop subject have a 5-zone range? Obviously not, because when these subjects are photographed and printed properly, both prints will exhibit the full range of print tones that we recognize as including the seven standard zone grays. It's clear, then, that every subject has seven zones, regardless of its luminance range in stops, because if this were not the case, it wouldn't be reproduced properly in a full-scale print. Therefore, as we've concluded before, zones and stops are not always equal."
This statement correlates with much more with my experience using Zone System. Even though Adam's originated ZS I give some priority to Davis since he provides a much more thorough explanation using sensitometry, the chassis underpinning ZS.
There are some important points of note before we get started. First, in order to clearly demonstrate how this flexible relationship between Zones and Exposure Values depends on the nature of the scene and the desired outcome of the final images' tonality I will have to use a number of graphs. I also need to use only one rigidly defined negative to print process because each film/print combination has unique results but also to keep this post short. Secondly, I need to introduce an unfamiliar term to many, the Subject Luminance Range. The Subject Luminance Range is the exposure range of the subject and therefore could contain a wide range of values; a high contrast scene may have 10 stops of luminance range from the object the darkest object to brightest object. The general assumption is that when a photographer supplies a number such as the Luminance Range they are identifying the darkest and brightest objects they want rendered with detail in the final image and how great the range of exposure is in stops between these two objects. For ZS practitioners they commonly want these objects in Zone II (darkest Zone that still has texture and space) and Zone VIII (lightest Zone that still has texture and space). The total number of zones from II to VIII is 7 zones which is where Phil Davis is getting his 7 stop quantity in the definition above.
To start somewhere with the utmost basics take a look at this simplified photographic imaging chain for film:
Since everything in this chain must be tailored to the limits of the human eye all exposure range limits must be worked out from the end of the chain to the beginning. The image below illustrates how finding a capture medium's luminance range requires one to work backwards through the photographic chain; the limits of the display dictate how the limits of the capture medium regardless of its dynamic range, which in turn provides a subject luminance range the photographer must work within.
In the cases where the photographer cannot adjust the exposure range of their subject then they must alter their photographic process to record a greater or lesser subject brightness range while still working within the limits of the display medium.
Since I work in motion picture my chosen example materials will be negative stock Vision3 500T 5219, and Vision Color Print Film 2383. First, I will perform a conventional analysis of 2383 to determine the exposure range of the print film and how look at how Zones are displayed under projection. In order for this post to be clear I moved the data from Kodak's Tech Publications into my own graphing program. This allows me to make each unit on the x and y-axes the same size, mark the axes in 0.3 increments which is a whole stop change in exposure or density, and also provide a useful grid.
Kodak Vision Color Print Film 2383 - A very steeply curved stock with a very high density in order to provide an image that extends outside the dynamic range of the adapted eye in the movie theater such that there is a rich black, brilliant white and rich midtone range.
Starting with the print stock I determine the range of useful densities from the toe to the shoulder using methods I learned in Beyond the Zone System. The minimum useful density, which typically defines the limit of Zone VIII, is located at the Base + Fog (where the toe bottoms out) plus 0.2 log density. This locates the minimum density at coordinate 0.24, 0.24. The maximum useful density, which typically defines the limit of Zone II, is found by taking 90% of the maximum density of the shoulder. This produced coordinate 1.33, 3.67. The difference between these two points on the Exposure Scale axis is a log exposure of 1.2 or 4 stops.
Same chart but showing how the exposure range of the stock is very narrow - log 1.2 or 4 stops - when looking at the x-axis. However, this is spread out into quite a wide range of rich tones under projection.
The total amount of density the print covers in stops is 11.4 stops, which is well beyond the dynamic range of our eye under dark surround conditions. This is exactly why the projected image contains a full range of tonality. While the image above is trying to help relate the print to our eye this would technically require the use of the characteristic curve of our eye to demonstrate how the the image would appear to have linear steps of tonality from black to white.
Moving on, now that we know the narrow exposure range of the print film, a log exposure of 1.2, we can use this to determine the exposure range of the negative.
The magenta-forming layer of Kodak Vision3 5219 with normal development. I have moved the data from the Technical Publication to a graph with the same size axes as the print stock curve used above.
Using the limits of 2383 we can see where these intersect the sensitometric curve of 5219 under normal development (I'm using only the magenta-forming layer of the film). These limits can then provide useful information about the luminance range of a scene and therefore ZS info. Notice that this film holds exactly a subject luminance range of 7 2/3 of a stop (the 200:1 ratio from my previous posts!).
As with the print I identify the lowest useful minimum density by going 0.2 log density steps above the B+F. (N.B. On the negative this determines the start of Zone II on the curve.) From this value I derive the coordinate -2.68, 0.78. We can't perform the same procedure as the print stock for locating the useful maximum density because negative film has an incredibly long shoulder that maxes out at a density far beyond anything the print can contain. That's fine because we use the acceptable log exposure range of 2383 to define the highest useful density. 0.78 plus 1.2 equals 1.98. This gives the coordinate -0.5, 1.98.
Despite the two graphs being analyzed separately the relationship between the negative and print can be easily understood by turning the print stock graph 90 degrees clockwise. Doing this helps better reveal how the step of contact printing the negative to the print stock transforms all the tonalities and how they are displayed to the human eye.
From Lorenz, Zakia and White's famous New Zone System Manual (1976, 11). Notice the delightful statement at the bottom that ties together the photographic system and the mind of the photographer.
This cartoon illustration really helps spell out how tonality is transferred from negative to print and how the limits of the print define the ideal Subject Luminance Range for the scene. So let's look at a real world example using 5219 with Kodak's recommended normal development
Notice how this illustrates my claims in previous posts; the DR of our vision is about 8 stops and the photographic chain is established to capture a Subject Luminance Range of about 8 stops and then display the image in such that a manner that all the Zones with detail are within the DR of our visual system. Everyone will always begin Zone system discussions in these lighting circumstances because they are about the average luminance range of light on a sunny day. When the scene is of average contrast, film development is "normal" and matched correctly to the exposure limits of the print then a Zone does equal close to a 1 stop change in exposure.
We can see how true this is by laying a Zone System scale on the slope of the negative's curve and see how much we have to expand or contract it in order to fit Zones II through VIII at the minimum and maximum useful densities.
By putting this ruler above the slope of the negative and then stretching the rules so that Zones II and VIII are at the limits of the Subject Luminance Range I can see just how much the tonality is adjusted to fit the exposure range of the print. In this case, Kodak's recommended normal development is just a touch lower than normal contrast so each Zone has been stretched slightly greater than 1 stop. (Notice where each Zone falls in relation to the vertical grid lines.) This difference is slight enough as to be negligible in practical working conditions so basically the 1 zone equals 1 stop relation holds.
However, the lighting ratio of a scene is realistically not always going to match up with the useful Subject Luminance Range of the system. This requires cinematographers and photographers to use lighting to adjust for this fact, but changing the developing time of the negative in order to capture a greater or lesser range of exposure is also accepted practice. (For the time being I want to set aside discussions of how changing development times impacts film grain.)
Let's say, for instance, that the luminance range the photographer wishes to hold is greater than 8 stops because there is a delicate texture in a cloud. In terms of Zone definitions they are moving the delicate highlight from Zone IX to Zone VIII so that it is rendered on the print. By pulling the film's development this lowers the contrast of the film and allows the densities from that bright highlight to fit within the Exposure Range of the Print.
Kodak 5219 pulled one stop. Notice how the exposure range the negative transfer to the print is 9 stops. This data was extracted from a sensitometry test performed on 5219 during Fall 2015 semester of my Science of Cinematography class.
Since transferring these recorded densities to the print will cause the Zones to expand we can lay our ruler along the slope of the curve and see how the Zones have been expanded as the contrast has been softened.
Notice how each Zone is now stretched to about 1 1/3 stops each. This is useful information to know when working in the field because now one can take light meter readings and know where objects will fall tonally in the final print.
In comparison, it is worth analyzing at the opposite case where a photographer needs to increase contrast on a foggy day. Below is 5219 pushed 2 stops in development. You can see that the Subject Luminance Range that fits the print is now lower contrast - 6 1/2 stops of range.
Laying the Zone System ruler on it we can see how the contrast of the image will be increased and how each Zone has shrunk to about 2/3 of a stop for each Zone. This is not terribly dramatic but it revealed to me that this particular stock does not alter its tonality characteristics when pushed as dramatically as when pulled.
Once again, despite the contrast of the scene the photographer changes the negative such that it fits the same Exposure Scale of the print stock giving a full black to white print. Looking at how the Zones relate to exposure now we find each zone is less than a stop.
Through this sensitometric analysis of Zone System we can arrive at the conclusion that 1 stop equaling 1 Zone is not a dogmatic truth, but rather changes based on the contrast ratio of the scene and how the photographer wishes to treat the tonality in their system. The relationship also changes based on films, developers, and the print medium. For digital technology this would be changes to the camera settings, curves used in Photoshop and the electronic display. Zones may be one stop in Ansel Adam's definition, but this is certainly not the case in practical work. This led Phil Davis to provide this critical new definition of Zones in the glossary of his book (1988, 213).
Zone: An ambiguous term. In this book, any one of the several divisions of the gray print scale that represent separate, consecutive luminance of 1 stop in the normal subject. In subjects of other than the normal 7-stop range, each print zone represents one seventh of the total SBR, whatever it is.
So to return to the question I've asked in previous posts, is this a mistake on Ansel and Archer's part in creating and explaining the Zone system? Well, partially, but then again the purpose of ZS is to provide a system to photographers that grounds their medium to the visual perception of brightness and also give them control over their tonal rendering without getting too bogged down in math or graphs. In some sense I should be laughing at myself for making this system precise by trotting out a bunch of math and graphs. But this is the beauty of ZS, that it provides useful tools that empower the photographer and are flexible to their unique vision without the weighty complexity of sensitometry. However, I can defend myself by pointing out that in order to clarify technicalities I must rely on the graphs and mathematics.
So why should everyone on blogs and forums make such a strong claim if they lack evidence? One would imagine anyone using ZS would discover through their photographs taken on low or high contrast days that they are expanding or contracting Zones to compensate for the change in lighting ratio. Nontheless, I think there are two reasons for this; first, the people who deeply understand ZS practice their photography but don't feel the need to shoot their mouths off online. Second, many of the books and blogs I find discussing a digital ZS typically fail to describe it in it's entirety. For instance, most forget that the first step is visualization and skip straight to Zone definitions, and many leave out the intricacies of understanding what changes were made in the computer and how they related to the subject as encountered at the moment of exposure. This is all well and good as a shorthand approach but no one should make bold sensitometric claims from a partial explanation. Lastly, I think the fluid nature of Zone appearances and their relation to exposure are more easily apparent to those who learned with analog. Without an LCD screen and a histogram we lived and died through our light meter. Extensive ZS tests provide us critical information to take out into the field to assist in metering. For instance, my information for 5219 in my notebooks looks like this:
The EI values were also calculated during 5219 stock tests during the Fall 2015 semester of Science of Cinematography.
Here is a nice visual representation of the expansion and contraction of Zones that helps with visualization.
Digital capture in RAW does not require one to make a decision in the field about how the image must be processed, this is done later in a computer. By shifting that decision to later and making it deceptively simple the photographer's understanding of what range of exposures were recorded and how they were effected by the curve applied in the computer obfuscates the process. I'm not saying this is bad, but that it does create the conditions for a disengagement of the mind. All progress involves a sacrifice and while it may be easier to change the image in post there is a problem of disconnecting from a deep understanding of the conditions one encounters in the act of taking a photo.
My purpose in addressing this one claim should not be viewed as an excoriation of those who make this mistake, or for those who espouse or use a shorthand version of ZS. My hope is that by taking this one single sentence, and exploring it in such detail photographers will be more inspired to not take everything they read online as gospel (even with my claims) and really pay close attention to their process. The wealth of information produced and available to us on the internet is immense and provides easy answers, but this should never be a substitute for performing one's own research.