Beyond the Digital Zone System

Ansel Adams
Ansel Adams by F. Malcolm Grany, circa 1947-1951

Definitions

What is a zone?

Zones are exposure values, assigned Roman numerals centered on V for the exposure indicated by a light meter.  Once again:

It is essential to remember the basic relationship:  if we take a reading from a single-luminance surface and use the indicated exposure settings, we are giving Zone V exposure for that surface, and anticipate a negative density Value V and a print Value V (middle gray) representing that surface . . . .  To determine the remainder of the scale, then, 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.
— Ansel Adams, The Negative (1981, 48-49)

Side note—I came across the following in Practical HDRI by Jack Howard:

I’m going to keep this easy, and deal with a relative scale throughout this book, where EV -1 equals a full-stop change from your metered median exposure, which I will describe as EV 0.  EV +2 is two full stops from your metered median exposure, and so on.

This is exactly what zones are:  a relative exposure value scale, translated into Roman numerals.  EV 0 is zone V, EV -1 is zone IV, and EV +2 is zone VII.

See also The HDRI Handbook 2.0:  High Dynamic Range Imaging for Photographers and CG Artists by Christian Bloch:

Photographers who are used to Ansel Adams’s zone system will instantly recognize that one EV span equals one zone.  If it would make you feel more comfortable, you could substitute these terms for the rest of the book.

One often sees zones defined differently, usually as fixed intervals on the image scale, independent of the underlying exposure:  “zone VIII is gray with texture.”  I hate to belabor the point, because the zone system or whatever system one uses is just a tool, a means to an end; but it is Ansel Adams who defined one zone as one stop on the exposure scale, and who said that the same zone may look different in different media.  If people want to redefine zones, fine; but they should specify that they are making up a new system, and not using “the” zone system.

The zone system

We have already seen Ansel’s description of “the zone system in a nutshell” in the introduction to The Negative:  relating subject luminances with print values.  Some more quotes:

[In the chapter called “Exposure,” referring to different ways of metering a scene:]
These limitations can be overcome using more specific readings of subject luminances and relating them to our knowledge of materials to control the values in the final print.  Such a method is the Zone System, to be discussed in the next chapter.
— Ansel Adams, The Negative (1981, 36)
The Zone System allows us to relate various luminances of a subject with the gray values from black to white that we visualize to represent each one in the final image.  This is the basis for the visualization procedure, whether the representation is literal or a departure from reality as projected in our “mind’s eye.”  After the creative visualization of the image, photography is a continuous chain of controls involving adjustment of camera position and other image management considerations, evaluation of the luminances of the subject and placements of these luminances on the exposure scale of the negative, appropriate development of the negative, and the making of the print.
— Ansel Adams, The Negative (1981, 47)
The Zone System is a practical expression of sensitometry, the science that relates exposure and density in photography.
— Ansel Adams, The Negative (1981, 84)
The Zone System correlates essential information, including effective film speed, subject luminances, meter, lens, and shutter calibrations, and film processing, along with your own concepts and recognition of image qualities in a subject.
— Ansel Adams, Polaroid Land Photography (1978, 127)
The Zone System is a practical application of the principles of sensitometry.
— Ansel Adams, Polaroid Land Photography (1978, 137)
ZONE SYSTEM.  A framework for understanding exposure and development, and visualizing their effect in advance.  Areas of different luminance in the subject are each related to exposure zones, and these in turn to approximate values of gray in the final print.  Thus careful exposure and development procedures permit the photographer to control the negative densities and corresponding print values that will represent specific subject areas, in accordance with the visualized final image.
— Ansel Adams, Examples: The Making of 40 Photographs (1983, 177)

My working definition, which attempts to include the essential elements of the zone system while at the same time applying to any photographic medium:  the zone system is a practical sensitometry in which subject luminances are assigned to specific exposure zones, and the subsequent photographic process controlled, so as to produce the intended image values.

Minor White
Minor White by David Vestal

Side note:  to visualize or previsualize?

Ansel always used the word “visualization” to describe the seeing of the final image in the mind’s eye, and considered “previsualization” a redundancy.  Minor White called the initial seeing “previsualization,” as opposed to subsequent “postvisualization.”

Previsualization:  Visualizing the photograph while studying the subject.
Postvisualization:  When printing a negative remembering back to the plan for the photograph.  Or when projecting forward to new combinations.
— Minor White et al., The New Zone System Manual (1976, 8)

Next:  so what is the zone system?