Zone system
From Wikipedia, the free encyclopedia
The zone system is a unique approach to film exposure and development invented by Ansel Adams and Fred Archer in 1939 or 1940. The zone system provides photographers with a systematic method of precisely defining the relationship between the way they see the photographic subject and the results they achieve in their finished works. In a sense, the zone system plays the same role that color management does for digital photographers. It allows for a direct correlation between the visual world and the final photographic print.
Contents |
[edit] Misconceptions
Unfortunately, the zone system gained an early reputation for being overly complex, difficult to understand and impractical to apply to real-life shooting situations. Two facts account for this misunderstanding: the first is that Ansel Adams, as the chief exponent of the zone system until the 1980s was a gifted artist but tended to assume more technical knowledge than the average student who approached his workshops or books had. Also, the zone system was initially designed for use with large format cameras where individual sheets of film could be processed separately. This allowed photographers to apply the zone system method to each subject discretely, which is an ideal approach not easily applied to roll film cameras that, until the digital revolution, dominated photographic practice.
One other misconception about the zone system is that it does not apply to color or digital photography. In fact, the zone system is conceptually extremely simple and because of certain limitations inherent to traditional and digital photographic materials, any photographer who achieves consistent quality in their work has to be using some variation of the zone system whether they are aware of this or not.
[edit] Dynamic range
What makes the conceptual basis of the zone system necessary is that modern photographic papers and current digital light sensors are very limited in the range of tonal values they can render. If a photographer were to double in steps the amount of brightness he used to expose photographic papers, depending on the grade of paper or variable contrast filtration he is using, he can only go between 6 to 12 steps (or stops) before the paper would stop recording any difference between one stop and another. Another way of saying this is that the dynamic range of photographic papers is limited to a ratio of very roughly 1 to 512. (It is interesting to note that in the earliest days of photography, printing papers had much longer scales. The trade off is that they were also much less responsive to light).
On the other hand, through a complex process of biochemical adaptation and our pupils adjusting, the human eye can perceive an extremely wide range of tones from the darkest value we can see, to the brightest light we can tolerate. The dynamic range of the human eye can be 1 to 1,000,000.
This means that photographers must bridge this gap through a method that allows for the final prints to approximate the way the world looks to our eyes. The zone system does this by providing photographers with a simple way to control the contrast of the film negatives in their cameras.
[edit] Principles
Contrast control of this kind is made possible because the amount of exposure the film receives has its primary effect on the darker parts of the photographic subject. The amount of time that film is developed controls the density of the lighter parts of the subject. This classic rule was stated in this way: “Expose for the shadows and develop for the highlights”. By first properly exposing their film, and then either increasing or decreasing their film development times, zone system photographers can, within limits, produce negatives that will print beautifully, regardless of how contrasty or flat the original subject happened to be.
Careful and committed photographers came to understand the above-described principles through the process of trial and error long before the zone system was formulated. The real genius and contribution of Ansel Adams and Fred Archer was creating a way for photographers to easily translate the range of tones they could see into a visual ruler that could be used to measure various subject tonal ranges in a predictable and practical way. This process is known as “previsualization” and it depends upon three related ways of defining something called a “zone”.
[edit] Zones, the Visual World and the Print
Imagine all of the tonal values that can be seen, or can appear in a photographic print, represented as a continuous gradation from black to white.
From this starting point zones are formed by first:
Dividing the spectrum into ten equal sections.
Blending each section into one tone that represents all the tonal values in that section.
Numbering each section with Roman numerals from 0 for the black section to IX for the white one.
[edit] Zones as Texture and Detail
In terms of the texture and detail we see in the world around us, there are three types of zones:
- Zones that are either pure white (Zone IX), or empty black (Zones 0 & I) and therefore have no texture and detail at all. These zones are used to visualize and represent extremely dark or pure white objects in a photograph.
- Zones that have a limited amount of texture and detail that are used to represent very dark or light objects that are slightly textured (Zones II and VIII).
- Zones with full texture and detail that make up the greater part of most photographs (Zones III, IV, V, VI, and VII).
The textured zone scale has traditionally been represented in the following way:
[edit] Measuring Zones
Zones represent amounts of light that double as the zones become lighter and halve as they get darker. In this sense, zones are equivalent to all other photographic controls. One zone equals one stop or one EV meter number. It also represents halving or doubling the ISO number. This equivalency allows the photographer to measure the contrast of any scene with f/stops, meter numbers, or zones. For the purposes of the Zone System they are all the same.
[edit] The zone system of exposure
A dark surface under a bright light can reflect the same amount of light as a light surface under dim light. The human eye would perceive the two as being very different but a light meter would measure them as exactly the same. For this reason, light meters are designed to render any tonal value they measure as Zone V. As noted above, each zone is equivalent to one whole aperture stop or shutter speed step so, by combining these two facts the zone system provides photographers with a very simple and reliable way to properly expose any photographic subject:
- The photographer needs to previsualize the area of the subject he would like to be a dark value with full texture and detail, or Zone III, in the resulting print. The correct rendering of Zone III is important because if dark textured areas of the subject end up as zones below Zone III they will appear underexposed.
- He then carefully meters the area previsualized as Zone III and makes a note of the meter’s recommended exposure.
- One needs to remember that the meter’s recommended exposure would render the chosen area as Zone V instead of Zone III. To correct for this the photographer would simply shoot subject using an exposure that was two stops darker than the meter’s recommendation.
[edit] The zone system of development
Every combination of film and developer has a recommended “normal” development time that will result in a negative that has contrast equal to that of the subject. In other words, this normal development time would result in a flat negative when photographing a low contrast subject, and a contrasty negative when photographing high contrast subjects
Proper development means understanding how to either increase or decrease the film’s development time to allow flat or contrasty photographic subjects to print well on contemporary photographic papers.
The zone system provides photographers with a way to measure the contrast of photographic subjects in terms of the zone scale which makes clear if the film requires more or less than “normal” development. These are called either “Normal Minus (N-)” or “Normal Plus (N+)” development times. The specific times for N+ or N- developments are either determined by doing systematic tests, or using development tables provided by certain zone system text books.
[edit] Digital
The zone system can be used in digital photography in a similar way to how it is used in film photography. The important difference is that while with traditional film photography (i.e with negative film) one exposes for the shadows and develops for the highlights, with digital one exposes for the highlights and post-processes for the shadows. Until recently, digital sensors had less range than color film, which, in turn, has less range than monochrome film. There are more and more exceptions in the digital world. One of the first ones was Fujifilm's FinePix S3 Digital SLR, which has a sensor specifically developed to overcome the issue of limited dynamic range. The CCD is able to expose at both low and high sensitivities within one shot by assigning a honeycomb of pixels to different F-stops of light. This effectively allows for an image to have information from a darker middle gray and a lighter middle gray, plus the dynamic range surrounding them. The Hasselblad medium format sensors followed then, which are able to decode 16 bits of color and expanded light information. Now, most of current Digital SLRs have 12 or more often 14 bits in their RAW image format and can achieve a 10-stop dynamic range (or very close), with moderate noise interfering with signal in lower zones. It is also possible to overcome the problem of limited dynamic range by creating multiple exposures of the same scene. The inherent problem with digital is that any pushes or pulls in brightness alter the amount of noise that appears in the final image (in a similar manner as film grain build in pushed areas). While making the image darker usually does not hurt too much, increasing brightness may have severe effects on final image quality. This is overcome by shooting the same scene twice, once exposed for the shadows, and once for the highlights. The image is then overlapped and masked appropriately (tutorial example) so that the resulting composite represents a wider gamut of colors and tones. [edit]
[edit] 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.
[edit] See also
[edit] External resources
- A basic explanation
- David Kachel's Front Door Learning and teaching the Zone System, plus novel development and darkroom techniques
- The Zone System An easy and very practical guide to the Zone System, by photographer Ken Rockwell.
- A simplified zone system, also very practical
- Clarkvision More about digital dynamic range
