The zone system for black and white photography enables you to visualize what the final picture will look like before you make the exposure. Luminance is the many reflective qualities of the subject. Understanding the relationship between the subjects luminances and the way in which those luminance values are rendered by photographic material will make you a better photographer. The procedure consists of accurately measuring those reflective values, visualizing how they should be translated into black and white print values, and then controlling negative exposure and development to achieve the desired result. It is a way to better understand how photographic materials respond to exposure and development, and will help you avoid unpredictable and complicated darkroom manipulations to achieve an optimum print. But the zone system is best when used on individual negatives. With roll film that is not possible. Ideally you would apply unique exposure and development times to each individual picture to achieve the desired print. But where an entire roll is processed in the same solution and for the same time, you have to make a few compromises and adjustments.
For example you can limit the images on a single roll to subjects of similar luminance values. By carrying two or more camera bodies or film backs, one for high-contrast subjects and another for low-contrast subjects and then by developing accordingly, you can create images that better reflect how you experienced and visualized each subject. Here are some ways in which I incorporate the zone system into my workflow when shooting medium format and 35mm film.
In the zone system scale, zone 0 represents maximum black and zone X represent pure white. There is no discernible textural detail in those areas. Zone V represents 18% gray, zone lll good shadow texture, and zone Vlll good highlight texture. All meters will give the f-stop and shutter speed combinations to produce a zone V density at what ever they are pointed at. (If you measure only the bright white fabric in a wedding gown or a black cat in a coal bin and set your exposure accordingly, both subjects will be rendered as the same 18% gray in the resulting 2 pictures) So to produce the true tonal value of the cat and see good textural detail, I would place my metered value of the cat on zone lll, because zone lll represents good visible shadow detail. The cat then must be underexposed by 2 stops from what the meter recommends, so that area will record as a zone lll value in the print. [note: a spot meter is best because you can meter important parts of the scene separately from a distance]
The principle of "expose for the shadows and develop for the highlights" is true as altered development times will enable you to compact or expand the highlight densities of any subject into the printable range of photographic paper without changing the shadow densities.
To begin, you would pre-visualize the scene in terms of tonal values and decide the darkest area of tone where you want to see some detail. You then meter those areas in the scene. In this church interior for example, using the spot meter in a Leica M5, I selected and metered the dark areas on the front of the altar and front of the small pipe organ, and placed them on zone lll to show textural detail in the shadows. That determined my exposure.
I felt an enveloping light and wanted to see the rich detail on the altar and organ while not losing detail in the stained glass windows. It was a sunny day outside and the windows measured a full 6 stops brighter than the shadow areas previously selected for zone lll placement. This put the window detail outside the printable range of the paper indicating that an adjustment be made during development to hold highlight detail in the final print. By reducing the development time of the film I was able to condense the exposure scale by one stop and hold the detail in the windows while leaving the tonal values in the shadows unchanged. Shadow density was determined by the exposure, highlight density was determined by the development.
One thing to remember is our eyes perceive things differently from sensitized film. It's important not to think of your subject only in terms of metered luminance values. You must think in terms of printed tones, how you visualize those tonal relationships, and how they will be expressively translated onto photographic paper. In order to use the zone system effectively it's necessary to first find the effective speed (ISO) of your chosen film using your meter, camera and lenses so you can determine what normal, normal-plus and normal-minus development times are. In part 2, we'll examine a simple test to determine the operational exposure value to assign to a film using your personal equipment.