Zone system

Originally designed as a tool for instruction while Adams and Archer were teaching at the Art Center School in Los Angeles, Adams went on to popularize the method. While Adams' focus was on monochrome (black and white) photography using medium and large-format cameras, many elements of the method have also been applied to color and smaller formats, such as 35mm.

The zone system was developed in conjunction with the concept of visualization. (Adams often called this "previsualization," though he later noted that the term is a redundancy.) The finished print was visualized before the picture was taken, based upon the carefully measured luminosity range of the scene and an intimate knowledge of how film and print paper could render that scene.

Together, the zone system and visualization allow photographers to translate the light from a scene into specific densities on negatives and paper, thus giving them better control over the finished photograph.

Overview for monochrome materials

0: Pure black
: I: Near black
: II: Dark gray / black
: III: Very dark gray - the lowest zone with distinct shadow detail
: IV: Medium dark gray
: V: Medium gray (equal to Kodak's 18% Grey cards)
: VI: Mid-tone gray
: VII: Light gray
:VIII: Gray / white - the highest zone with distinct highlight detail
: IX: Near white
: X: Paper base (pure white)

What makes the zone system so useful is the ease with which it translates desired effect to camera settings. Light meters will return the proper aperture (f-stop) and shutter speed to expose the metered area at 18% middle grey - equal to zone V. Each zone above or below zone V corresponds to one f-stop. So, for example, if a photographer desires the shadow values of the ground below a bush to be a very dark tone, but still holding detail (zone III), he or she would close the aperture two stops from the light meter's reading of the shadow area. The smaller aperture results in less light hitting the film and thus in darker shadow areas.

Film

Monochrome (black and white) film can record a light intensity range of about seven zones. The luminosity range of a scene, however, from the darkest shadows to the brightest areas, may be substantially greater or less than seven zones. Thus information can be lost in contrasty scenes due to the limited sensitivity range of film, or the range of film can be under-utilized in flat scenes.

The zone system manages this by:

• identifying what the film will record at different levels of exposure to the scene;
• processing the film in ways that modify the sensitivity range it ultimately records.

Ansel Adams' famous book The Negative lays out preliminary calibration and darkroom tasks, taking test pictures of the gray card at different exposures, simulating the zones, and then developing the film. Following his directions will bring to light any miscalibration of equipment and variations of developer chemistry due to the local water supply. Once completed, the photographer will have correctly calibrated equipment and a solid understanding of the zones.

Development can be expanded (underexposed and overdeveloped) or contracted (overexposed and underdeveloped). This has the effect of expanding or contracting the contrast range recorded on the film, and can be applied to scenes that have a luminosity range unequal to the dynamic range of the film. Expansion and contraction also affects the contrast of the final image, and the zone system helps the photographer to have full control over these techniques.

Color film has less range than monochrome, and sensors in digital cameras even less (although digital hardware is quickly improving). Some principles of the zone system, however, can be applied to color photography, largely in the area of light measurement and knowing what one can expect from color materials.

Darkroom

Ansel Adams generally used selenium toner when processing prints. Selenium toning can alter the color of a print and act as a preservative, but Adams used it subtly, primarily because it can add almost a full zone to the tonal range of the final print, producing richer dark tones that still held detail.

The zone system requires that every variable in photography, from exposure to darkroom production of the print, be calibrated and controlled. The print is the last link in a chain of events, no less important to the zone system than exposure and development of the film. With practice, the photographer visualizes the final print as the shutter is released.

See also