The Zone System is a set of techniques that allowed photographers the greatest possible control over the characteristics of black-and-white film and the subsequent display print. Adams authored five (impenetrable) instructional books entitled The Basic Photo Series: The Camera, The Negative, The Print, Natural Light Photography, and Artificial Light Photography.
This little exposé is my tribute to Ansel Adams and my gift to those who struggled as hard as I did in trying to understand his method. It is also a salute to those like Minor White and Fred Picker who attempted to clarify the Zone System with equally challenging approaches.
The first step for the photographer involves what Adams called previsualization. He describes the genesis of this insight as occurring on a rigorous climb in 1927 to a vantage point from the west ridge overlooking the spectacular granite formation of Half Dome in Yosemite Valley. Adams made an exposure on a 6 1/2” x 8 1/2” glass plate following his routine exposure pattern. He then had a further thought about how this subject would appear as a photographic print; and realized he could add considerable drama to the image by using a dark red filter to deepen the values of the sky. With his last plate, he made the exposure with the red filter.
In a late revision of his book The Negative, Adams shows a comparison of the two images:
(The Negative, Ansel Adams; New Photographic Series/Book 2, New York Graphic Society, 1981, pp. 4, 5)
From this point Adams attempted to anticipate how the values of the subject would translate to the values of the print prior to releasing the shutter on the camera. Previsualization was the first step in the process and can be described by imagining the grayscale interpretation of the subject represented by a set of ten tonal values or Zones that represent its brightnesses. Each Zone, or shade of gray, is separated from its neighbor by an exposure of double or half the amount of light. Of course, there are many more tones in a picture than ten, but this approximation handily matches the dynamic range of panchromatic film.
The above illustration shows how the values may be found in a picture. Two challenges can be predicted at this point. First, the photographer is facing a full-color subject and must begin to translate the colors into neutral brightness values. This is more difficult at first than one would imagine, and devices such as monochromatic viewing filters were often used to assist in the process. Secondly, how can the individual values be measured? All light meters were designed to interpret the subject values in an overall fashion, reducing the extremes to an average value of middle gray and a suggested exposure to achieve it.
But the Zone System was intended to consider the unique values of each subject and properly record the tones for the best possible print. Adams used an S.E.I. Exposure Photometer with a sensitivity angle of 1˚, a precursor of the Pentax Spotmeter and Minolta Spotmeter instruments that were eventually to follow.The steps in previsualization involved carefully measuring the brightness values of the subject and comparing those values to the photographer’s plan for the print. If the subject values matched the response of film, correct exposure was calculated and the job was done. The development of the film was carried out normally and a good print could be made on gelatin silver paper of normal contrast.
But if the subject values did not match the print interpretation, other steps could be taken to achieve the tonal values required by the negative.
Previsualization and Exposure
This is an idealized representation of the “Characteristic Curve”; a plot of the response of film to light. The vertical component represents density after exposure and development. The horizontal component represents the logarithm of exposure. (Logarithms are simply a shorthand way to represent large numbers.) The Zones are indicated along the base, and the grid is squared off to represent the changes that occur when the exposure is doubled from left to right. Zone VI is achieved by exposing twice as long as Zone V. (See the note below on Light Meters.)
Is it coincidence that both shutter speeds and apertures also double or halve the setting adjacent to them?
1/30 sec. is half as long as 1/15 sec. and twice as long as 1/60 sec.
Aperture f/8 transmits twice as much light as f/11 and half as much light as f/5.6
1/30 sec. is half as long as 1/15 sec. and twice as long as 1/60 sec.
Aperture f/8 transmits twice as much light as f/11 and half as much light as f/5.6
The Toe of the curve–the shadows represented by Zones 0, I, and II–have little separation from one another. This is an inherent problem in silver halide emulsions and is called “Reciprocity Failure”. Compare to Zones III to VII–the Straight Line Section–and it may be noted that an equal amount of density is achieved each time the exposure is doubled = Reciprocity exists. In the highlights–the Shoulder–Reciprocity fails again. The result is a tendency for the deepest shadows and brightest highlights to merge together producing tonal differences but a lack of detail in these areas.
Interestingly, as film is processed, the shadow areas, which have received the least amount of exposure, will achieve complete development fairly early in the development cycle. As the development time progresses, the highlight areas build up density progressively–even beyond what may be expected from exposure. Silver grains continue to aggregate in the highlights. If development were allowed to continue overlong, the highlights would become so dense that no light would pass through them in the printing process. (See note on Film Density.)
Recognizing the characteristics of exposure and development, the Zone System concludes that shadows can only be affected by exposure, while the highlights are affected by both exposure and development. The maxim to follow is:
Expose for the Shadows, Develop for the Highlights
The most significant shadow is Zone III–the first deep value that indicates some texture. It is Zone III that establishes the correct exposure for the subject. The plan recommended is to expose the shadows correctly, and follow a development procedure that will produce just the right amount of density in the highlights. The light meter is the instrument that is used to determine the basic exposure and indirectly to predict the development time.
It works like this: all light meters have to be calibrated to something. Light meters are averaging devices rather than spotmeters and will indicate an exposure resulting from averaging the highlight and shadow values together. So the meter calibration is called middle gray; the value that results when darks and lights are averaged together. Spot meters are calibrated for middle gray also, but they can select small sections of the subject. (See notes on Light Meters.)
A light reading is taken of the important shadows. This “middle gray” reading must be re-calculated to record those values as Zone III. Since each f/stop or shutter speed change is equivalent to a Zone change, simply counting stops produces the desired result. Which way? Since shadows in the negative are less exposed than the middle values, two stops of exposure must be subtracted. Consider the hypothetical example:
Shadow reading: 1/125 sec @ f/5.6 this meter reading of the shadow produces a Zone V (middle gray) tone
1/125 sec @ f/8 subtracts one stop of light and produces a Zone IV value (either shutter or aperture may be used)
1/125 sec @ f/11 subtracts two stops and produces a Zone III value, this is the correct exposure for the image
Now it is important to determine how this exposure affects the highlights. A new light reading is taken of a bright value, say one that would appear best as Zone VIII:
Highlight reading: 1/125 sec @ f/32 using this reading would record highlight as Zone V
1/125 sec @ f/22 overexposes the first reading by one stop and moves the highlight to Zone VI
1/125 sec @ f/16 overexposes two stops and moves the highlights to Zone VII
1/125 sec @ f/11 overexposes by three stops and records the highlights corrrectly as Zone VIII
In this case both the shadows and the highlights are correctly recorded with the same exposure. Conclusion: the subject has a normal contrast range and the negative would be developed normally.
Rather than the tortuous calculations described above, it was always possible to purchase a stick-on label to a spotmeter that simplified the placement procedure:
What happens if the highlight exposure is different? If the highlight values fall too low on the tonal scale after establishing the correct shadow exposure, overdevelopment is required to build up the density appropriately.
The chart at left indicates an image with a short exposure scale that can be remedied by developing longer to bring the highlights to their normal position.
If the highlight values fall too high on the tonal scale, development must be reduced to prevent these values from reaching negative densities that would not print correctly.
The chart at left presents an image that would result in higher than printable highlight densities. These values can be diminished by shortening the development time.
Substantial testing is required of the Zone Sytem practitioner to confirm the the following:
• Correct calibration of the light meter and the ISO of the film, this is tested, not assumed
• Normal development time for the film and chemistry
• Length of development time required to increase highlight densities by one stop, by two stops
• Length of development time required to reduce highlight densities by one stop, by two stops
When confronted with extremes of lighting that could not be accommodated with exposure and development alone, Adams also utilized further techniques such as pre-exposure of the film to a blank value to produce a bump in the shadows for greater detail. Another technique was the water-bath development for extreme contrast reduction. Film was dunked in developer for 30 seconds, then placed in a water bath for a minute. The developer that soaked into the highlights was utilized quickly, while the developer in the mid-tones and shadows was allowed to continue. In this way the highlights did not become as dense as they normally would.
_____________
Bear in mind the following precepts:
Film always wants to see the same amount of light; it’s sensitivity is measured as an ISO value and cannot be changed.
All light meters (averaging and spotmeters alike) are calibrated to evaluate the brightness of the light and produce a middle gray (Zone V) exposure.
The shadow values of a picture are determined by exposure alone, while the highlight densities can be manipulated by the length of development time.
ISO (International Standards Organization) was also once called ASA (American Standards Association) and batches of film are manufactured to meet the tolerances of sensitivity to light governed by these systems. Film sensitivity can be slow or fast. Fast film will allow pictures to be made under weak lighting conditions. Slow film requires longer exposure times. You might correctly hypothesize that the controlling factor of sensitivity is the size of the silver grains in the film’s emulsion. To simplify, imagine that each exposed grain of silver halide in the emulsion will eventually be transformed to a particle of metallic silver. Larger silver halide complexes produce larger grains of resultant silver. The same amount of light energy is required to expose a small halide as a large one. Therefore the desired density can be achieved with less light if the grains are large.
Light Meters are presented with a dilemma, measuring the values of a subject which may be dark or light and translating the values into a usable exposure. The solution is to average the lights and darks together in order to produce an exposure that the film may tolerate within its range of sensitivity. Imagine a disk that is painted half black and half white and is spinning in front of the meter. (Hurter and Driffield used exactly such an approach and attached the disk to the flywheel of a sewing machine.) This is a range of extremes, black and white, averaged together; the result is middle gray. A problem emerges when the subject values are the same: a section of a blackboard in a classroom, a section of a white bulletin board, and a section of a smooth adobe building in shadow are three subjects comprised of one value. If a composition were were made of each of these subjects separately and if the indicated meter exposure were followed, each negative would appear identical in tonal value. But if all three subjects appear in the same image, they will assume their correct relationships due to the averaging together of the values by the exposure meter. Meters like the Zone VI Pentax Spotmeter were provided with a zone scale to assist in the calculation of the exposure.
Film density is predominantly determined by the size of the developed silver grains. Developing the film is a chemical reaction where an exposed silver halide particle is reduced to metallic silver by the magic of chemistry. The exposure to light has forced a subtle molecular change in the silver halide molecule: something in the nature of an electron migrating to a different orbit. Exposure produces an invisible Latent Image that is made visible by development. As with any chemical reaction, the results of development are modified by the variables of time, temperature and agitation. You can predict the influence of these variables with a simple experiment: dissolve a teaspoon of sugar in a glass of iced tea. If the sugar is simply added and settles to the bottom of the glass, it will eventually go into solution. If the tea drinker is impatient with that method, stirring (agitation) will hasten the reaction and shorten the time required. And if the tea is hot instead of iced (temperature), the sugar will dissolve immediately. It is usually intended that this reaction be allowed to go to completion; nobody wants the last swallow to be sweeter than the first, so drinking is delayed until the sugar is completely dissolved. In processing film, however, a complete reaction would result in highlight densities that are too severe. Developing film is an ongoing reaction because in areas where there was ample exposure (highlights), silver grains continue to aggregate and grow with increased development. Manufacturers of black and white film always included a processing chart that indicated normal time of development. Note that this density increase only occurs in the highlights, because no amount of overdevelopment will effect the minimal exposure that the shadows received. Shadow values are controlled only by exposure; highlight densities are controlled by development.
The first goal is producing the best possible negative as a foundation for printing the image as the photographer previsualized it. Once mastered, the Zone System allows photographers to consistently control the tonal range in the negative. The system works best with sheet film, which can be exposed and developed one piece at a time.
In spite of the fact that the dynamic range of digital camera RAW exceeds that of fine grained film, there still seems to be a surprising amount of interest in using film and in the Zone System; a Google search for "Zone System" yielded 383,000 hits! If Ansel Adams were alive today, I guarantee he would be testing the latest digital cameras and inkjet printers.
____________________
Here are the resources I used in my study of the Zone System. The information provided above is an amalgamation of what I've read and my own testing and practice.
The Negative, Ansel Adams; New Photographic Series/Book 2, New York Graphic Society, 1948, 1971, 1981
Zone System Manual, Minor White, Morgan & Morgan, 1968
The New Zone System Manual, White, Zakia, Lorenz, Morgan & Morgan, 1976
The Print, Ansel Adams, Basic Photo Series, Morgan & Morgan, 1971
Zone VI Workshop, Fred Picker, Amphoto, 1974
The Fine Print, Fred Picker, Amphoto, 1975
It works like this: all light meters have to be calibrated to something. Light meters are averaging devices rather than spotmeters and will indicate an exposure resulting from averaging the highlight and shadow values together. So the meter calibration is called middle gray; the value that results when darks and lights are averaged together. Spot meters are calibrated for middle gray also, but they can select small sections of the subject. (See notes on Light Meters.)
A light reading is taken of the important shadows. This “middle gray” reading must be re-calculated to record those values as Zone III. Since each f/stop or shutter speed change is equivalent to a Zone change, simply counting stops produces the desired result. Which way? Since shadows in the negative are less exposed than the middle values, two stops of exposure must be subtracted. Consider the hypothetical example:
Shadow reading: 1/125 sec @ f/5.6 this meter reading of the shadow produces a Zone V (middle gray) tone
1/125 sec @ f/8 subtracts one stop of light and produces a Zone IV value (either shutter or aperture may be used)
1/125 sec @ f/11 subtracts two stops and produces a Zone III value, this is the correct exposure for the image
Now it is important to determine how this exposure affects the highlights. A new light reading is taken of a bright value, say one that would appear best as Zone VIII:
Highlight reading: 1/125 sec @ f/32 using this reading would record highlight as Zone V
1/125 sec @ f/22 overexposes the first reading by one stop and moves the highlight to Zone VI
1/125 sec @ f/16 overexposes two stops and moves the highlights to Zone VII
1/125 sec @ f/11 overexposes by three stops and records the highlights corrrectly as Zone VIII
In this case both the shadows and the highlights are correctly recorded with the same exposure. Conclusion: the subject has a normal contrast range and the negative would be developed normally.
Rather than the tortuous calculations described above, it was always possible to purchase a stick-on label to a spotmeter that simplified the placement procedure:
What happens if the highlight exposure is different? If the highlight values fall too low on the tonal scale after establishing the correct shadow exposure, overdevelopment is required to build up the density appropriately.The chart at left indicates an image with a short exposure scale that can be remedied by developing longer to bring the highlights to their normal position.
If the highlight values fall too high on the tonal scale, development must be reduced to prevent these values from reaching negative densities that would not print correctly.
The chart at left presents an image that would result in higher than printable highlight densities. These values can be diminished by shortening the development time.
Substantial testing is required of the Zone Sytem practitioner to confirm the the following:
• Correct calibration of the light meter and the ISO of the film, this is tested, not assumed
• Normal development time for the film and chemistry
• Length of development time required to increase highlight densities by one stop, by two stops
• Length of development time required to reduce highlight densities by one stop, by two stops
When confronted with extremes of lighting that could not be accommodated with exposure and development alone, Adams also utilized further techniques such as pre-exposure of the film to a blank value to produce a bump in the shadows for greater detail. Another technique was the water-bath development for extreme contrast reduction. Film was dunked in developer for 30 seconds, then placed in a water bath for a minute. The developer that soaked into the highlights was utilized quickly, while the developer in the mid-tones and shadows was allowed to continue. In this way the highlights did not become as dense as they normally would.
_____________
Bear in mind the following precepts:
Film always wants to see the same amount of light; it’s sensitivity is measured as an ISO value and cannot be changed.
All light meters (averaging and spotmeters alike) are calibrated to evaluate the brightness of the light and produce a middle gray (Zone V) exposure.
The shadow values of a picture are determined by exposure alone, while the highlight densities can be manipulated by the length of development time.
ISO (International Standards Organization) was also once called ASA (American Standards Association) and batches of film are manufactured to meet the tolerances of sensitivity to light governed by these systems. Film sensitivity can be slow or fast. Fast film will allow pictures to be made under weak lighting conditions. Slow film requires longer exposure times. You might correctly hypothesize that the controlling factor of sensitivity is the size of the silver grains in the film’s emulsion. To simplify, imagine that each exposed grain of silver halide in the emulsion will eventually be transformed to a particle of metallic silver. Larger silver halide complexes produce larger grains of resultant silver. The same amount of light energy is required to expose a small halide as a large one. Therefore the desired density can be achieved with less light if the grains are large.
Light Meters are presented with a dilemma, measuring the values of a subject which may be dark or light and translating the values into a usable exposure. The solution is to average the lights and darks together in order to produce an exposure that the film may tolerate within its range of sensitivity. Imagine a disk that is painted half black and half white and is spinning in front of the meter. (Hurter and Driffield used exactly such an approach and attached the disk to the flywheel of a sewing machine.) This is a range of extremes, black and white, averaged together; the result is middle gray. A problem emerges when the subject values are the same: a section of a blackboard in a classroom, a section of a white bulletin board, and a section of a smooth adobe building in shadow are three subjects comprised of one value. If a composition were were made of each of these subjects separately and if the indicated meter exposure were followed, each negative would appear identical in tonal value. But if all three subjects appear in the same image, they will assume their correct relationships due to the averaging together of the values by the exposure meter. Meters like the Zone VI Pentax Spotmeter were provided with a zone scale to assist in the calculation of the exposure.
Film density is predominantly determined by the size of the developed silver grains. Developing the film is a chemical reaction where an exposed silver halide particle is reduced to metallic silver by the magic of chemistry. The exposure to light has forced a subtle molecular change in the silver halide molecule: something in the nature of an electron migrating to a different orbit. Exposure produces an invisible Latent Image that is made visible by development. As with any chemical reaction, the results of development are modified by the variables of time, temperature and agitation. You can predict the influence of these variables with a simple experiment: dissolve a teaspoon of sugar in a glass of iced tea. If the sugar is simply added and settles to the bottom of the glass, it will eventually go into solution. If the tea drinker is impatient with that method, stirring (agitation) will hasten the reaction and shorten the time required. And if the tea is hot instead of iced (temperature), the sugar will dissolve immediately. It is usually intended that this reaction be allowed to go to completion; nobody wants the last swallow to be sweeter than the first, so drinking is delayed until the sugar is completely dissolved. In processing film, however, a complete reaction would result in highlight densities that are too severe. Developing film is an ongoing reaction because in areas where there was ample exposure (highlights), silver grains continue to aggregate and grow with increased development. Manufacturers of black and white film always included a processing chart that indicated normal time of development. Note that this density increase only occurs in the highlights, because no amount of overdevelopment will effect the minimal exposure that the shadows received. Shadow values are controlled only by exposure; highlight densities are controlled by development.
The first goal is producing the best possible negative as a foundation for printing the image as the photographer previsualized it. Once mastered, the Zone System allows photographers to consistently control the tonal range in the negative. The system works best with sheet film, which can be exposed and developed one piece at a time.
In spite of the fact that the dynamic range of digital camera RAW exceeds that of fine grained film, there still seems to be a surprising amount of interest in using film and in the Zone System; a Google search for "Zone System" yielded 383,000 hits! If Ansel Adams were alive today, I guarantee he would be testing the latest digital cameras and inkjet printers.
____________________
Here are the resources I used in my study of the Zone System. The information provided above is an amalgamation of what I've read and my own testing and practice.
The Negative, Ansel Adams; New Photographic Series/Book 2, New York Graphic Society, 1948, 1971, 1981
Zone System Manual, Minor White, Morgan & Morgan, 1968
The New Zone System Manual, White, Zakia, Lorenz, Morgan & Morgan, 1976
The Print, Ansel Adams, Basic Photo Series, Morgan & Morgan, 1971
Zone VI Workshop, Fred Picker, Amphoto, 1974
The Fine Print, Fred Picker, Amphoto, 1975
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2 comments:
You know, if the universities get wind of your website, they'll let all their instructors go and just refer their students to your site. They'll save millions.
What a phenomenal article! I remember reading, then re-reading "The Negative", then trying to apply it's principles with a large format camera. An exhaustive effort . . .
I've seen some HDR imagery from friends Tony Schanuel and David McCarty, both former devotees of the Zone System, who have created absolutely stunning digital photographic imagery at high noon. I was shocked when I saw it.
I think properly using and understanding digital imaging principles is just as much of an artform as the negative ever was.
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