In video production, just like in photography, the right exposure is essential for a good outcome. Most cameras today come equipped with light meters and other aids to properly expose an image. However, it is not always wise to rely on the automatic settings your camera provides. While for the most part an internal meter can do the job and give you a good exposure, there are situations in which you need to be in control. One of the ways we can control the exposure is by using the zone system.
We have often found ourselves in very difficult situations that present a definite challenge in terms of exposure. For example, a brightly lit area near a dark zone. Think of a sunny day: the bride is wearing a bright white dress that reflects the bright sunlight. The bridegroom is right next to her in a handsome black tuxedo. Depending on how you frame the shot, your automatic meter may expose for the black tux and overexpose the white dress. Or, it may expose for the white dress and underexpose the black tux. So, there you are: you need to make a decision and take control, or your shot may not turn out to be so good after all.
You may encounter a similar challenge if you have reflections in your shot. Let me explain. Let’s say that you are taking a shot of a dark surface under a bright light (a challenge similar to the one just described). The dark surface, however, has a reflection from the light. That can be a nightmare for your light sensor, because now the dark surface will be metered as bright as a lighter one under a dim light source. Again, you need to take control and make the proper decisions for your exposure.
Understanding the Zone System
Think of a scale of grays that goes from pure black to pure white. In the middle you will have a middle gray. This scale is usually divided in 11 zones, in which 0 represents the pure black, 5 represents the middle gray, and 10 represents the pure white.
In this scale, you will have the following shades:
- Pure black. (0)
- Near black. Some tonality, but no texture. (1)
- Textured black. This is generally the darkest part of the image in which some detail is recorded. (2)
- Average dark objects. Low values showing adequate texture. (3)
- Average dark foliage. Dark stone. Landscape shadows. (4)
- Middle gray. Clear North sky, dark skin, or average weathered wood. (5)
- Average Caucasian skin. Light stone. Shadows on the snow in sunlit landscapes. (6)
- Very light skin. Shadows in the snow with bright side lighting. (7)
- Lightest tone with texture. Textured snow. (8)
- Slight tone without texture. Glaring snow. (9)
- Pure white. Light sources and specular reflections. (10)
The two extremely important zones are zone 3 and zone 8. This is because zone 3 is the lowest exposure showing adequate details and zone 8 is the highest zone showing adequate detail. The zone system gives you a fairly simple method for rendering the main subjects as you desire. After you identify the key element in the scene, you want to set your exposure in such a way as to place it on the desired zone in the zone scale. The other elements in the scene then fall where they may.
For example: If your main subject in the scene should be in zone 3, but because of a reflection it is metered in zone 5, you will want to expose the shot two stops less than the light meter recommends in order to place it where you want it, in zone 3. This is because if you follow your light meter you will not have sufficient details in the shadows.
Negative and Positive
When we used to work with negatives, the most important details were the shadows. This is because a shot that is underexposed would leave the shadow areas transparent in the film, with no details. Once these details are lost, they can never be regained. So, you would want to expose your dark areas so that they match at least zone 3. On the other hand, light objects, which appear dark in the negative, would still have some detail even if slightly overexposed, and you could then use various methods to bring them out as you process the image.
Video cameras, however, record positive images. In this case the important zone is zone 8. In fact, once you have lost details in the light areas, you can never regain them. So, the goal is to expose the image so that your lightest subject does not go beyond zone 8 unless it is a light source that is expected to be bright and without detail. If the image is slightly underexposed, you can then still recover the details in the dark areas in post-production.
Using a Wide Dynamic Range
In order to record sufficient details both in the dark as well as in the light areas, many professionals opt for a wide dynamic range. Images captured in that way appear a bit flat, but the important thing is that they have details in the shadows and details in the light areas. Contrast and color grading is then managed in post-production.
In the example mentioned before, of a bride in a bright white dress and the bridegroom in a black tuxedo, a way to resolve the exposure conflict is to use a wide dynamic range that will allow you to expose the dress so that it will match zone 8 at most, and the black tux so that it will match at least zone 3. In this way, you will be able to retain details in both areas of your scene. Then, in post-production, while you color grade you can also adjust the gamma and contrast as needed to make the image look appealing.
Learning from a Master
If you wish to study the images of a master in the art of photography and the zone system, you may wish to study the images produced by Ansel Adams. Looking at his masterpieces, your will see many examples of how he was able to render the various tones and textures without losing important details.
Well, we may not all be like Adams, but that does not mean that we will not benefit from the principles of the zone system. So run some experiments and practice your exposure in difficult situations, so you will be prepared for that precious but challenging shot. Indeed, the zone system may be useful, but it is not the whole answer to the many challenges we encounter on a daily basis when filming. That’s why experience and practice are not only precious but irreplaceable.