Used mainly by film users. It is a system of defining the relationship between the photographers visualisation of the scene and the final printed results. The system uses a calibrated scheme of light through to dark tonal “zones”. These are used to calculate the best exposure in camera. Then, they are used to carry that record through to the chemical development of the film. This helps the photographer develop the photo by reference to the zone system tones rather than guess work. This makes for a more consistent result and one that is tonally faithful to the real scene.
Ansel Adams and Fred Archer developed the Zone System. Adams in particular was very interested in the way he visualised the scene as a part of making the photograph. He made his images with a clear picture in his mind of what he wanted the outcome to look like. This visualisation technique is used in a wide range of sports and business situations. The pre-visualisation directs the performer to particular goals. It helps them to reach a desired end result. The Zone System was designed to aid the achievement of a visualisation by calibrating the lights and darks in a scene. Next, that record is carried forward to calibrate the development of the film.
Exposure metering and the Zone System
When the Zone System was drawn up, light meters were unable to separate varied areas of luminance. This produced an ‘average result’ for the image. It ignored the fact that there could be big differences between the lightest spot in a scene and the darkest.
Any scene also has a middle zone of luminance. A dark area in bright light may reflect the same amount of light as a light area in dim light. The eye sees the detail of each differently. The exposure meter sees only the total light level. It renders them as the same light level. The eye sees best by distinguishing the contrasts. The Zone System helps the photographer to set the exposure to bring out these variations.
Adams realised that to get the best out of a scene he could visualise how he wanted that range of illumination to look in his prints. So he set out to find a way to capture images using a zonal chart which described the differences in luminance. Using the Zonal System he could develop the image using a known scale to bring out the same qualities in the final image. It would also allow him to manipulate those qualities when developing the image. This could increase the visual impact.
The zones themselves describe the typical luminance of elements in a scene thus…
Adams worked with film. He used wet processing – chemical developing of the images. So he was able to categorize parts of his scene as tones on the chart. Then he would work out a precise time to expose for that level of luminance. To bring out the contrasts properly, he assigned the exposure to one of the zones. After calculation he was then able to work out how many Stops he should compensate for to get the best detail in the dark spots. Each zone varies from the next by a factor of two. Thus a Zone-1 exposure is 2x that of Zone-0. This is the same through out the range. A one-zone change is equal to one stop. This told him how long he should expose the film in-camera. It also made it easy to do exposure compensation. He could vary his exposure times to deepen or lighten the darker tones (or lighter ones).
Next, in processing, he would use those calculations to work out what levels of chemical developing would be required to replicate the real scene. Depending on his test prints, he could also use the Zone System to manipulate the development to bring out more lights or darks in the final print.
The system depended on detailed calculations. Each stage of the work flow (in camera, on to developing) is precisely matched by a calculation for the exposure and chemical bathing times. It allowed for precise control of the processes. This precision enabled tonal replication of the original scene. It also enabled precise manipulation of the tones in the scene by using the appropriate development times and chemicals.
The Zone System in modern situations
The Zone System is mostly used in film and chemical developing. It required a level of dedication to the calculation of illumination and record keeping. Those records were then used in precise calculations for developing. Modern digital technology has largely removed the need to do this work.
The electronic meters in a camera can do ‘average metering’. However, spot meters are common in quality DSLRs. Any of the spots in the viewfinder can take a precise exposure reading of approx one degree around the spot. The result is that you can set the overall exposure for the shot against that standard.
The user can therefore pick the area of the shot to expose for in the viewfinder. Then they can set the chosen spot to be the exposure meter for the shot. The DSLR calculates the exposure time for this luminance level. The the Zone System is replaced by the precision of the on-board computer.
In addition you can use exposure compensation to change the overall exposure to take account of strong areas of light and dark in the scene. This gives the photographer in-camera control of the image creation based on the exposure. The camera does those calculations for the user.
Modern digital processing techniques allow precise adjustment of light and dark in the image. This can be changed in very localised areas of the image as well as globally. Such manipulation was possible in chemical developing. However, the precision of modern digital techniques makes use of the Zone System largely unnecessary.
Despite digital precision, there are some people who continue to work with the Zone System using digital gear.
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