exposure - How do the 11+ stops of dynamic range from a modern DSLR fit into the 10 stops of the zone system?

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.

Answer

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 D_max 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.