Zone System

The zone system is a term from analog black and white photography and refers to a technical- scientific method for optimizing the key factors in the production of black and white photographic negatives individual.

In contrast to the photochemical standard development processes of analog color photography, the development of black and white material is extremely variable and thus allows a targeted, differentiated translation of light brightness by not only the exposure level but also the development time adapted to the scene being photographed in analog differences in density of negative silver films will. Thus, the zone system in the classical sense, is limited to the processing of single negatives, as they are used in large-format cameras. In practice, the type of development to be used will be limited to a few options (N- 2, N -1, N, N 1, N 2), intermediates ( N- 1.3) are very atypical. Therefore, the zone system can be used in medium format cameras with interchangeable magazines without problems.

The aim is primarily a systematic exploitation of the chemical- technological potential of the analog black and white image storage, especially from the point of maximum Tonwertreichtums and its consistent implementation up to the final positive image formats - but also the optimal control of the photographic craft that does not " Misses " permitting, leaves nothing to chance and thus reduces the high material costs in the big picture photography to the necessary.

Basic principles

In his well-known in the art book trilogy, the American photographer Ansel Adams published (1902-1984) which he often attributed, Zone System ', which in an individual adjustment process of the dominant motif contrast shooting conditions, the exposure range of the store black and white film used, the density range of the negative after his photochemical development as well as the final positive production in the laboratory process is. It comes down to a carefully calculated control this crucial for the image process operations recording / Image storage / film development / positive process with the help of a theoretical construction of 11 (zone 0 to zone 10 ) by densitometry accurately calibrated trunk gray values ​​, which differ in their darkness each time by a light value differ.

For the analogous preparation of a supervisory frame ( positive ) to the negative-positive process, two separate operations are necessary in principle: the generation of a negative than the actual image storage in a suitable camera and the transfer of the contrast range of the photochemically developed negative in the positive process on the photo paper.

Here, the negative density range of the film and the printing range of the photographic paper differs considerably - as the classic zone system only "normal" working with the paper grade, the density range of the negative must be adapted by each modified development parameters to the printing range of the photo paper.

Originally propagated by Ansel Adams system included only the production of a technically perfect negative - later they tried, the further process steps up to the final deduction involve.

Pre-visualization and contrast control

A central role for the concept is played by the concept of pre-visualization. The aim of this pre-visualization is a kind of inner conception of the image effect along with the associated photographic- technical consequences before the actual recording process. Want the photographer, for example, evoke a dark, working with heavy tonal mood, a normal exposure would miss with the associated average brightness of a subject the targeted interpretation.

To achieve the intended image effect rather certain parts of the subject would have to be reproduced clearly darker than normal. To achieve this goal, it is necessary to keep the dynamic range of the recording during the entire processing chain in view.

The zone system takes into account that the dynamic range of a photo paper is less than that of a film or the actual motive. This means that, for example in high-contrast landscapes, the scale of tone or gray values ​​from black to white technically can not be transferred from the negative to the paper.

By controlling the development parameter is used to adjust the negative contrast: A prolonged exposure of the film and subsequent reductions in development causes lower contrast ( " smaller" tonal range ), the image effect is rather soft in the direction. A shorter exposure in combination with a prolonged development can be sluggish at motif contrasts emerge the black and white values ​​more clearly, that causes an increase in contrast.

Zone system with digital technology

The considerations of the zone system apply in a similar way for other recording methods, this means also for CCD or CMOS sensor of a digital camera, the computer monitor and the printing, for example with inkjet or laser printer. The expression ( the paper form of the image) again has the most limited contrast range. A monitor may be another, but compared to the original limited contrast range. The digital image processing provides with appropriate software much wider scope as gray values ​​can be adjusted individually or in relation to each other, what can be done in the darkroom only with great difficulty or not at all. A creative transformation is possible, the boundaries for image manipulation, however, are fluent.

Another advantage of digital photography is that shortly after the recording of a histogram or the monitor display can be assessed roughly whether there is over-or underexposure. Aperture and shutter speed can be changed as long as with an analogue camera especially with steady images to the intended contrast ratios are achieved. Thus no need - as with the negative or slide film - until the film development are awaited to assess whether correctly or the wishes was exposed accordingly.

With a software several differently exposed images can be combined. If some of the brightness range of the scene exceeds the sensitivity range of the image sensor, shots of different exposure to the computer can be assembled to drawing in light and in dark image sections to ensure (see HDRI generation of bracketing ). The result is a so-called HDR image before with high dynamic range. In order to display these images in any conventional media, they must be compressed in its dynamic range and matched with a tone-mapping process.

Some digital image sensors have not only the required fine gradation ( bitrate of the luminance signal ), but can compress extreme contrast ratios without loss of information even by a sequence logarithmically graded exposure times of the individual pixels.

Classification of zones and exposure

Adams has divided the reproducible range of contrast of a photo in 11 ( Inscribed with 0 to 10) regions or zones. The distance between the zones corresponding to each of all the aperture setting ( 1EV ). Zero stands for deep black without drawing ten referred to pure white without drawing. Five corresponds to the so-called neutral gray with 18% reflection. The laboratory copyable on photo paper range includes the nine zones from I to IX; by drawn, detailed area containing the zones II to VII

If using a spot light meter ( in camera or light meter ), a part of the subject appropriate to the exposure value the Zone V represents (18% neutral gray ) - all exposure meters are calibrated to this. However, it is possible to assign this part of the subject to another measurement value or a different zone to change the effect on the photo: If the zone are displayed in dark, but with drawing in the picture, it could be classified as zone III. Shows the meter, for example, 1/30 and F s to 8.0, consequently would be 1/30 f 16 in use. All other parts of the subject of the picture fall, depending on the selected exposure also in a different tonal range or a different zone. So is conditionally controllable, in which brightness or contrast with what each picture important parts of the subject are reproduced.

If such an image- important part of the subject in the selected exposure in the zone IX, so white, almost without drawing, only a dull image effect would occur, which may not meet the expectations of the photographer. Thus, there is no "correct" or "correct" exposure - rather the photographer exposure values ​​that result in an image that evokes the intended effect on the viewer chooses.

The exposure values ​​are configurable by design, the desired photographic and artistic effect as well as the development -dependent and may vary up or down. The boundaries between good recording, suitable photographic technology to the demonstration of hidden details, artistic freedom and manipulation are fluid - a mist sun can be transformed, for example, in a sunset.

Exposure in practice

Adams led a variety of methods of calibration, contrast and other influencing and thus designed his large-format photographs. Not all are available in 35 mm film now most commonly used. The essence of the zone system can be realized, however, when a camera with manual setting is available.

A textured surface which corresponds to about a medium gray, about a doormat or a wall, with the selected camera film combination ( or the corresponding digital camera setting) added "normal" and fill the frame. It is found with regular exposure metering, for example exposure 1/30 f 8 This now corresponds to Zone V, now more shots are, for other zones, made with different exposure values ​​:

• Zone 0 1/125 f 22
• Zone I 1/60 f 22
• Zone II 1/30 f 22
• Zone III 1/30 f16
• Zone IV 1/30 f11
• Zone V 1/30 f8
• Zone VI 1/30 f5, 6
• Zone VII 1/30 f4
• Zone VIII 1/15 f4
• Zone IX 1/8 f4
• Zone X 1/4 f4

Of course, any other time and aperture combination according to the light level of the zone V recording be selected if it considers, for different zones, each respectively to the distance of an f-stop or time step (= 1 EV). Helpful, it is always to write down the number of each image together with exposure ( aperture and shutter ) and zone. By logging an experience can be built that can be accessed later on.

The recordings are now being developed in the desired, but previously roofed form or reproduced or projected, given in the simplest case just about the lab or printed. When deductions from the laboratory, it is necessary for the application of the zone system, to find a lab that offers the possibility to waive automatic exposure compensation, otherwise all deductions are again corrected to neutral gray. This should be obtained or determined by test, but it is usually possible at retailers. The eleven developed images (according to the above zones) now show the contrast range and the drawing of the selected reproduction chain; using the logs are also the values ​​traceable. There may be details, that is, the tonality and contrast, no longer fully visible even for the Zone III or Zone VII shows the last usable light drawing. So it is necessary or possible for any reproduction chain ( camera and lens on the film ( or sensor and a specific setting ) for positive / projection / screen) to make a bracketing. The results of this bracketing can be used for the design of recordings (visualization) in the future.

Experience shows that viewers recordings as "good" or "right" feel exposed, where the contrast range was exploited as possible. The recording technique for this would be to pay attention to (two) parts of the image that will be displayed in black without graphic details or white in the final image. The image- important parts of the subject should be in the intervening through painted area, the exposure frame after the zone system as far as possible be adapted to it.

Movies and color

In the negative films determined brightest usable zone can be selected as the base region ( on the film ), by means of the then corrected exposed. It is appropriate to that subject that is just with drawing dark ( = bright spot on the negative film ) should be displayed on the trigger, according to the example in zone III. Then the exposure is greater (ie, f / 4 instead of f / 8 or 1 /60 sec instead of 1/ 250 s ) selected two stops or time steps. Well, it is determined in which zone the brightest main subject is part falls. If it is within the determined by drawn range, the exposure is optimal.

With slide film, the lowest (lightest ) usable zone is selected as the base zone vice versa. This approach is also useful because in movies, the dark areas (for negative films according to the brightest parts of the image ) quickly " run " show more detail than the comparatively brightest ( darkest ) places.

The bright (or dark ) points can be in the post, if available, correct and better. A slight over-exposure from the negative film or slide film slight underexposure can therefore be tolerated in certain circumstances. Of course, in slides for projection as well as in the absence of processing option, the bright and dark borders must be elected immediately correct.

While the original zone system was mainly used for black-and- white photography, today mostly color films are common, also allow the below other design measures. The contrast correction with filters on the camera itself has become something uncommon to the color temperature contrast can be influenced. For modern films of the altered dynamic range must be considered in the zone system. In color films, the difference from the black and white contrast material is usually low, with slide films stronger. This, and the subjective effect of the color should be considered when the recording in the system area. The sensor of digital technology is in the range of hues in turn with the slide film comparable, added noise and other special features.

Boundaries of the zone system

The photographic work with the zone system was devised for working with a large format camera and the associated possibility of a single film development - it unfolds especially where their optimal potential, where the photographer has the time necessary to measure the subject and the subject contrast at rest with the spot meter to evaluate and to coordinate with the film development - mainly landscape, portrait or still life shots.

All areas of the subject, the work with small film formats and require a dynamic and fast photographic access, such as sports photography, street photography or reportage, are rather unsuitable for systematic work with the zone system.

Undeniably, however, is still the high didactic value of the zone system, with the aid of basic relationships are illustrated in black and white photography. Despite now available Gradationswandelpapiere and extremely powerful films, it is certainly useful as a foundation for an optimal technical mastery of the photographic craft and to make selective use of these photographic- technical means for sharpening of photographic expression.