Introduction and History

The Zone System was originally put together by the two great American photographers, Edward Weston and Ansel Adams. Edward Weston would 'pre-visualise' his photographs, taking meter readings from various different parts of the scene he wanted to photograph. From these, he would arrive at an exposure based on his idea of how the images should look, and a deeply intuitive sense of how the film would behave. Ansel Adams, who was of a more scientific persuasion, took these ideas, and built them into a more systematic framework, which is very useful for those of us not blessed with Edward Weston's extraordinary abilities! This framework is the Zone System. The System provides a means of understanding and controlling the response of camera film to various lighting conditions, and different levels of subject contrast. The result of this is to give the photographer a high degree of control over the finished result, and to provide negatives which are easy to print. Before getting down to the nitty-gritty of how it works, it's probably best to have a look at the way light meters work, and also to say a bit about simpler systems of metering, and their advantages and drawbacks.

What Light Meters Do

To start with, it is easier to understand metering if you take colour out the equation (don't worry - I'm going to put it back later), and think in terms of a monochrome image, where everything is rendered as a different shade of grey.

Correctly calibrated, a light meter will measure the amount of light coming from whatever object you point it at, and will recommend an exposure which would render that object as a middle grey in the final picture. This is based on the assumption that the tones in a scene will generally average out to grey. This gives us the simplest form of light metering; you take an average reading of the scene in front of you, and provided that the tones in that scene average out to a middle grey, a reasonable record of that scene will be made on the film.

This is fine so far as it goes, but it's not hard to see its limitations. If the scene in front of you does not average out to a middling grey, then the reading will be incorrect. For example, imagine a field of fresh snow. To give a sense of the brilliance of the snow, you would want to record it as a very light tone. However, the light meter has no way of knowing this, and recommends an exposure which records the snow as middle grey - giving a dreary, underexposed image. The same problem arises in reverse if you want to photograph a predominantly dark subject.

So, a more advanced approach to light metering involves being aware of this limitation, and finding ways to compensate for it. In the case of our field of snow, you might add a little to the meter's recommended exposure, to lift the tones. Or you might find a middle-toned object which is bathed in the same light as the field of snow (such as a rock outcrop), and take a meter reading from this, giving the meter something which you do want to be rendered as middle grey, and letting the other tones fall into place around this.

This is the approach adopted by a lot of serious photographers, and on the whole it works pretty well. Essentially, what the Zone System does is to take this approach and build on it, developing more of an understanding of how film behaves, and providing control over the tones recorded. Returning to the snowy field, the Zone System would enable you to decide exactly how bright and how detailed you wanted the snow to appear. It would also tell you how bright and detailed other objects in the same image (such as the rock outcrop, and the sky) would appear.

The 11 Zones and How to Meter Them

The basis of the Zone System lies in dividing the possible shades of grey rendered by film into 11 discrete densities, each separated by one stop¹, and known as Zones. The Zones are commonly numbered from 0 to X, as follows:

To place the snow on your chosen Zone, start by taking a meter reading from it. As I have described above, the meter will recommend an exposure which will record the snow as a middling grey; or, as we now know it, Zone V. So, to move the snow up to, say, Zone VII, you would add 2 stops to the meter's recommendation (you might want to go back over this bit and make sure you understand it fully, before continuing).

So far, so good. You are now able to decide just how you want the snow to look, rather than vaguely 'adding a bit' to the exposure. However, what about the other tones in the picture? What about the rock outcrop I mentioned earlier. What about the sky? Well, suppose we take a meter reading from the rock outcrop. The exposure the meter recommends turns out to be 1 stop more than the one we have set on the camera (i.e. the one which places the snow on Zone VII). In other words, the exposure we are giving the rock is one stop less than what the meter recommends for it. Remembering that the meter will always recommend an exposure that places the subject on Zone V, this means that, with the exposure we have chosen, the rock outcrop will be rendered as Zone IV, a fully textured dark grey.

Next, take a reading from the sky. Imagine the meter recommends an exposure which is one stop less than the one you have set on the camera. This means that the sky will be rendered as Zone VI, a fully textured light grey.

Where does this put you, then? Well, you now know that the tones in the picture will appear as follows:

Film Speed and Development

To use the Zone System effectively, you really need to know that your film is behaving as you think it is. A huge number of variables can affect the final density and contrast of a photograph. The calibration of your light meter, accuracy of shutter speeds and apertures, time and temperature of film development (how accurate is your thermometer?); these are just some examples. So, if you really want to know exactly what the film is doing, you need to carry out some tests. The tests I am going to outline here will take into account all possible variables, and enable you to set up a film exposure and development regime that is geared towards your own camera and darkroom setup.

If a film is to produce the results you expect it to, then two factors need taking into account: film speed (how much the film darkens for a given exposure to light) and contrast (the difference in film density between exposures to different amounts of light). Film speed is mainly a function of how the film has been manufactured, and is not something over which we have a significant degree of control.² Contrast is mainly affected by how much development the film receives, which we do have control over. So, for accurate metering, we need to be able to measure film speed, and control film contrast. This is why it is well worth while developing your own films. However, don't worry if you don't have facilities to develop your own film, you can still go some of the way - more of this in a bit. If you can measure two Zones on the film, comparing what they are with what you'd like them to be, then you have enough information to start working towards the correct film speed and contrast.

The two easiest Zones to measure and compare with their ideals are Zone I (just off black - no visible texture) and Zone IX (just off white - no visible texture). It is possible to devote entire films to testing alone, but for the ordinary photographer on a budget, I recommend including two test negatives on each film, and using the results from these to decide how to expose and develop your next film. From a reasonable starting point, you can usually get things tweaked to just about the right place within three or four films. And this is how you do it:

On each film, make two negatives of an evenly lit, evenly toned, textured surface. If it is a neutral colour, all the better (black and white films rarely respond equally to all colours of the spectrum). For the first negative, underexpose from the meter reading by 4 stops. The second negative should be overexposed by 4 stops. You now have two negatives on the film which, with the correct film speed setting and development time, would be on Zones I and IX. Next, you need to find out where they really are! Having developed the film, take the test negatives into the darkroom. The idea is to print the test negatives, and see what the results look like. This is why we test against Zones I and IX, as these are very easy to judge, when compared with pure black and pure white.

Choose a medium contrast (grade 2) paper. If you are working with multi-contrast paper, choose a grade in the middle of its range (usually grade 2.5). Start by getting the enlarger focussed correctly with a normal negative. Then, from the film with the test negatives on it, make a test strip of an unexposed part of the film - the edge of the film, or maybe the beginning or end. You are aiming for the minimum exposure which will render this as pure black - the darkest the paper will produce. By doing this, you calibrate the enlarger to the film³. Do several test strips, with finer and finer differences between the exposures - you are aiming to 'home in' on the correct exposure, and you should try to be pretty accurate about it. This is the most time consuming part of the test.

Once you have found the exposure which is just enough to render unexposed film as pure black (comparing the test strip with a piece of paper deliberately given a large exposure to ensure a pure black will help you here), make prints of each of the test negatives, giving these exactly the same exposure, paper contrast and development as you arrived at by testing the unexposed bit of film. You can now look at these prints, and decide if they fall accurately on Zones I and IX.

Let's start with the Zone I test. This should be just off black, with no visible texture. If it is indistinguishable from the pure black print you made earlier, then the film is not exposed enough. The film speed you are setting on your meter is too high. Reduce it by a half or third of a stop (whatever your meter allows), and repeat the test with the next film. If the print shows visible texture, it has been exposed too much. The film speed you are setting on your meter is too low. Again, adjust it, and repeat the test with your next film. In either case, keep the film development time the same. If the Zone I test indicates that a film speed adjustment is needed, there is no point in continuing with the Zone IX test until your next film.

If the film passed the Zone I test, then congratulations! You have the correct film speed set on your meter. You can now consider the film development time, and this is where the Zone IX test comes in.⁴ Compare your print of the Zone IX negative with a piece of unexposed, but fixed and washed, paper. If there is no difference (i.e. the Zone IX print is pure white), then the contrast of the film is too high, and you need to reduce development time on your next film. If there is visible texture, then the contrast of the film is too low, and you need to increase development time on your next film. When adjusting development times like this, I generally make a 20% adjustment each time. If this 'overshoots' on the next film, I then go back 10% the other way.

In terms of the sort of accuracy you are aiming for here, I generally reckon on being within a third or half of a stop (depending on what divisions your meter allows) of the ideal film speed, and within 10% of the ideal development time. If you try to be more accurate than this, the law of diminishing returns starts to make itself felt! If you cannot hit the ideal film speed and development dead on, then aim to err on the side of overexposure and under-development.

A Rather Surprising Discovery

Upon completing the above test, you will very likely find that your tested film speed is about half that given by the manufacturer. Don't worry, you haven't got it wrong! I'm not quite sure why, but the film speeds and development times recommended by film and developer manufacturers will generally amount to a considerable underexposure and over-development, by comparison with that which gives the best result for the Zone System. In fact, when shooting negatives for testing, I recommend that you start with a film speed of about half that given by the manufacturer. As for development time, for slower films (manufacturer's speed less than 400 ASA), I recommend starting with the development time recommended for downrating the film one stop. For faster films, the development time recommended for the film speed given by the manufacturer is usually a better starting point.

These starting points will also make quite good approximations if you want to use the Zone System, but really don't fancy all the testing. A friend of mine started like this, simply downrating his films one stop, and couldn't believe how much easier it made them to print. He said that good prints seemed to just 'fall out of the enlarger'.

A Bit More About Development

So far, I have given you a set of tests which take you towards a film speed and development time which give you the set of Zones described above; and if you are using roll film (i.e. 35mm or medium format), this is about as far as it goes. However, if you are using large format sheet film, so each frame gets individual development, you can take things further still, and start adjusting film development to the contrast range of each picture you take.

The way of developing film I have described is known as 'N' development, and generally gives the best compromise between coping with a wide range of subject brightnesses and keeping a good level of tonal separation. However, if the contrast of a scene is unusually high or low, you can, to some extent, compensate for this by deliberately under or over developing. For example, if you give the film extra development, so that Zone VIII shows as just off white, with no visible texture, this is known as 'N+1' development. Taking this further, if Zone VII shows as just off white, with no visible texture, then this is 'N+2' development. Similarly, degrees of deliberate under development are known as 'N-1' or 'N-2'. Obviously, to work out times for these different degrees of development would require further tests along the lines of those described above. Since I haven't actually used this technique myself (I only work with roll films), I won't go into any more detail here.

A Zone System for Colour Photography

So far, I've only talked about monochrome photography. It is possible, however, to use a Zone System type philosophy when taking colour photographs. With very occasional exceptions, I use commercially processed slide film for all my colour photography. I've found that, using the manufacturer's recommended film speed, a simpler Zone System, with a shorter scale, can be used:

I almost never use colour negative film, and given this type of film's great flexibility and margin for error, the Zone System is probably more sophisticated than necessary. However, being a creature of habit, when I have used colour negatives, I have still metered according to the Zone System, using the manufacturer's recommended speed, and this has consistently given me well exposed, printable negatives.

Conclusion

The Zone System offers a good way to take more control of your photographs, and to understand how your film is behaving. It removes the guesswork from photography, so you can concentrate on making images, without worrying about whether they'll 'come out right'. I firmly believe that metering a photograph is as much a part of the creative process as composing it. If you really want to express yourself fully through your photographs, no part of the process should be outside your control.

If you're a little daunted by some of the heavier aspects, like film testing, then start at a simpler level. Try downrating your films one stop (or get your lab to do this if you have them processed commercially). This will almost certainly make your negatives easier to print at one fell swoop. You can then maybe start thinking about metering separate parts of scene and placing them on the appropriate Zones, and build from there. This was how I got started, and I haven't looked back since!

Further Reading

'Elements' by Barry Thornton, published by Creative Monochrome, is an excellent and very readable introduction to the Zone System, and quite a bit else besides.


'The Negative' by Ansel Adams, published by Little, Brown, is an in-depth technical manual about negative exposure and development, which will give you a good understanding of how film actually works and behaves.