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Adams's Zone System uses 10 zones with the first zone being pure white and the last zone being pure black. The distance between each zone is one stop / 1EV, so if you place a black tone at zone 0 and increase exposure by 10 stops that black should be pure white.

Given that modern DSLRs can shoot 11+ stops of dynamic range, how does this effect the zone system? Surely a sensor with greater than 10 stops of dynamic range from pure whites to pure blacks needs a zone system containing more zones?

I'm not interested in a debate over whether the zone-system is useful in digital photography, but I have seen and read a lot of recent material explaining either the traditional version of the Zone System or simplified versions with less zones.

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That description only represents the "base setting", or "N" exposure, of the Zone System.

The idea that the Zone System revolves around 10 exposure steps is a vast oversimplification. There are, indeed, 10 (or, actually, 11) "zones", or major tonal values in the print, ranging from effectively unexposed white paper (at Zone X) to the paper's Dmax at Zone 0.

The "N" exposure corresponds to an exposure and development combination that will render those tonal zones on #2 paper at approximately 1 EV/exposure step per tonal zone, with a spot meter reading corresponding to Zone V.

One would normally, through testing, arrive at several other combinations of exposure and development in order to expand or compress the tonal variation. Again, the object of the game was to get a predictable basic print (without dodging or burning) on #2 paper, in order to eliminate as many variables in the process as possible. An "N-3" combination would, for example, capture 13 stops with a contrast range that would render as those ten tonal zones when printed. An "N+2" would spread 8 stops of scenic dynamic range over the same 10 zones. Practically speaking, N-3 or N-2 was often the limit of the film; attempting to develop to lower contrast would do funny things to the response curve, leaving you with no real printable picture (though it would be possible to scan the negative and fix the curve with modern digital processes).

Outside of the "N" exposure, you would have figured out compensations required for placing tones (other than Zone V). If you wanted to place a detailed shadow area in Zone III, you didn't necessarily reduce the spot-metered exposure by two stops; it may have been a stop-and-a-half for an N+1, or three stops for an N-3.

This, of course, applies primarily to sheet film, where you can expose and develop each frame taken individually. A roll film shooter using the Zone System would typically shoot at N-1 or N-2, just to be safe, then handle the contrast range variations using different paper grades or variable-contrast paper. (Increasing contrast when printing is trivial; trying to reduce contrast much would run you into the shoulder and toe of the response curve, leaving you with mushy shadows and highlights.)

In any case, the idea that the zones of the Zone System directly correspond to exposure steps in the scene is a misunderstanding based on only considering the normal "N" exposure/development combination. It is merely a predictable method to "expose for the shadows, develop for the highlights" with as close to a linear response curve as possible. The zones themselves describe values in the print, not in the capture.

The only real difference when translating to digital is that we now expose for the highlights and "develop" for the shadows. By that, I mean that a modern camera with a relatively high dynamic capture range will let you raise or drop the shadows pretty much at will (and you can place the midtones just about anywhere you want), but the important highlights with detail are the one thing you absolutely can't let go. And yes, the best of the modern cameras are very near to having the ability to capture the full range of the best you could do with film (modulo compression of tones in the shoulder and toe of the curve; digital is pretty close to perfectly linear across the whole curve). But it still remains for the photographer to arrange the captured range within the limits of the display medium (screen or print) - and that's what the Zone System is all about.

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The particulars will be different due to the increased capacity of modern cameras and typical display devices (A good LCD monitor has a slightly wider dynamic range than the photo papers Adams used and those we use today, for instance), but the basic concept remains the same: Divide the available dynamic range for your scene (within the limits of your capture device) with an eye to how much of that range can be squeezed into the range of your display medium without making it look unnatural. For photographing a very high contrast scene in Adams' time that meant taking a medium format B&W negative with a usable dynamic range of 14 stops, adjusting contrast by lengthening the exposure time slightly and shortening the development time of the negative and then tone mapping via dodging and burning the print in the darkroom to squeeze those 14 stops captured by the negative into the 6-7 stops or so that the paper was capable of differentiating.

Adams used eleven zones (0-10 inclusive is 11, not 10). Zone 0 represented the darkest capability of the printing paper. Zone X represented the lightest capability of the printing paper. Both Zones 0 and X could include an infinite number of stop or EVs in the scene. Zones I through IX were evenly spaced from deep shadows to highlights with Zone V being medium grey. Zone I and Zone IX included no texture, but were distinguishable from pure black and pure white. Only Zones II through VIII included perceptible details. But each of those zones do not necessarily equate to 1 EV present in the scene. This is probably the most misunderstood aspect of the zone system. from "Exposing for the Highlights" by Gisle Hannemyr:

Many texts on the zone system claims that the difference between adjacent zones are 1 EV (1 f-stop). This is not true. EVs and f-stops express relative difference in levels of light present in a scene. Zones express relative difference in levels of density present in a photographic print, which may or may not reproduce exactly the relative levels of the original scene.

Everyone thinks the zone system is about "correct" exposure. It is not. It is about visualising the image desired for viewing, and then backtracking through the process to use the exposure needed to produce the desired image. The heart of the Zone System for Adams, who worked with sheet negatives that could be individually developed, was the ability to expand or contract the contrast range of the negative in order to increase contrast and add impact to low-contrast scenes or to reduce contrast to hold detail in both highlights and shadows in high-contrast scenes.

If a scene metered more stops (than his paper could differentiate with a 1:1 correspondence between the number of EVs in the scene and the tonal range of the paper) between the brightest to dimmest parts of the scene for which Adams wished to preserve detail, then Adams would reduce contrast by developing for a shorter time. If a scene metered fewer stops than a 1:1 correspondence then he would develop longer.

One thing a lot of folks miss today when studying Adams is that he adjusted his zones, in terms of the EV value per zone, based on the total amount of contrast in the scene. He did this by using a lower or higher calculation for the sensitivity of his film and then compensating when he developed the negative to give higher or lower contrast from the same scene. Perhaps a lot of this was lost in translation when the Zone System was adapted for use by those who shot roll film, and thus did not have the ability to develop each frame individually the way Adams did with his sheet negatives.

Fortunately, in the digital age we can once again treat each exposure individually the way Adams and others were able to do. We can select the appropriate sensitivity (ISO) for each shot based upon the demands of shutter speeds and aperture, and then we can adjust the light curves in post to control the contrast. And we also get to play around with adding color filters to monochrome images after the fact as well as apply adjustments to white balance, selective color, and saturation that would have required a different customised film emulsion for each individual shot in the past!

With the ability of modern post-processing applications, you're not even limited by the camera's dynamic range. You can also combine multiple images exposed at different Exposure Values into a floating point file and then tone map that into the 7-10 stops that a modern LCD screen can display. We have various methods and various names for the different ways we can do this. We can even soft proof our file and squeeze it into the 6-7 stops or so (plus pure black and pure white on either end) that can be reproduced on physical prints.

The key difference between shooting sheet negatives, such as Adams did, and shooting digital files such as we do today, is that Adams "exposed for the shadows and developed for the highlights". With digital we more often expose for the highlights and then develop for the shadows.

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