Zone system
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The zone system is a photographic technique for specifying optimal film exposure and development invented by Ansel Adams and Fred Archer in 1941. 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. It allows for a direct correlation between the visual world and the final photographic print. The system is applicable to digital photography, although it originated when photography used only film.
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[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 and equipment. 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 originally used with large format cameras where individual sheets of film could be processed separately, allowing photographers to apply the zone system to each subject discretely. This ideal approach was not easily applied to roll film cameras that, until the digital revolution, dominated photographic practice.
Another misconception is that the zone system does not apply to color or digital photography. In fact, the zone system is conceptually extremely simple and can be applied to traditional and digital photographic materials.
Many photographers feel that if they don't have a large format camera allowing photographs to be developed individually they have nothing to gain from the Zone System. This isn't so; the Zone System can bring the tonal ranges within limits that can be recorded on the negative, so long as the camera allows exposure time and f-stop to be varied manually. In fact, 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 500:1, or 9 stops (29). (It is interesting to note that in the earliest days of photography, printing papers had much larger dynamic range, i.e. much longer tonal scales, which allow the print to have more detailed highlight and shadow detail, e.g. reproducing the lace in a white bridal gown while also reproducing the black satin and buttonhole details in the groom's tuxedo. 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 is approximately one million to one (107), or about 20 stops (220).
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 negative film requires sufficient exposure to bring out the details in the darker parts of the image, while development time controls the density of the lighter parts. This was stated in the classic rule: “expose for the shadows and develop for the highlights”. Proper exposure followed by adjustment of development time lets zone system photographers produce negatives that print beautifully, however contrasty or flat the subject (within reason).
Careful and committed photographers came to understand these principles through 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.
Note: You may need to adjust the brightness and contrast of your monitor to see the gradations at the dark and light end of the scales.
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 (Zone 0) and therefore have no texture and detail at all. Some texture can be recorded in Zones VIII (near white) and I (near black), though these zones will hold no useable detail. These zones are used to visualize and represent extremely dark or pure white objects in a photograph and are referred to as the textural range of exposure zones.
- 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 VII). This diminished range of exposure zones represents the dynamic range of exposure zones.
- However, for cinematography, in general parts of the scene falling in Zone III will have textured black, and objects in Zone VII will have textured white. In other words, contrary to the image below, if the words on a piece of white paper are to be readable, light and expose the white so that it falls in Zone VII. This is a general rule of thumb. Some film stocks have steeper curves than others, and the cinematographer needs to know how each one handles all shades of black-to-white.
- 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 just as in film photography. The important difference is that one exposes for the shadows and develops for the highlights when using negative film; whilst one exposes for the highlights and develops or post-processes for the shadows with either color reversal film or digital imaging.
Until recently, digital sensors had a much narrower dynamic range than color film, which, in turn, has less range than monochrome film. But an increasing number of digital cameras with wider dynamic ranges are appearing. One of the first ones was Fujifilm's FinePix S3 Pro digital SLR, which has their proprietary 'Super CCD SR sensor' specifically developed to overcome the issue of limited dynamic range, using interstitial low sensitivity photosites (pixels) to capture highlight details. 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 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, which can decode 16 bits of color and expanded light information, followed. As of 2007 most digital SLRs have 12 or 14 bits in their RAW image format, and have a dynamic range approaching 10 stops[citation needed], with moderate noise interfering with the signal in the lower zones.
It is also possible to overcome the problem of limited dynamic range by creating multiple exposures of the same scene (see High dynamic range imaging). The inherent problem with digital is that any pushes or pulls in brightness increase the amount of noise that appears in the final image in the same way as film grain becomes more noticeable in pushed areas. While making the image darker usually does not hurt too much, increasing brightness may significantly worsen final image quality. This is overcome by shooting the same scene twice, once exposed for the shadows, and once for the highlights. The images are then overlapped and masked appropriately ([1]) so that the resulting composite represents a wider gamut of colors and tones.
[edit] Darkroom
Ansel Adams generally used selenium toner when processing prints. Selenium toning acts as a preservative and can alter the color of a print; 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 shadow 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] References
- The Negative, Ansel Adams Basic Photography Series Book II ISBN 0821221868
- Zone System: Step-by-Step Guide for Photographers, Brian Lav ISBN 1584280557
- The New Zone System Manual, Minor White; Richard Zakia; Peter Lorenz; ISBN 0821221868
- Beyond the Zone System, Phil Davis ISBN 1584280557
- The Confused Photographer's Guide to Photographic Exposure and the Simplified Zone System, Bahman Farzad ISBN 0966081714
- The Practical Zone System, Fourth Edition: For Film and Digital Photography, Chris Johnson ISBN 0240807561
[edit] External resources
- A basic explanation
- David Kachel's Front Door Learning and teaching the Zone System, plus novel development and darkroom techniques
- A simplified Zone system for making good exposures, also very practical
- Clarkvision More about digital dynamic range
- A Simplified Zone System A Simplified Zone System
