We’re lucky. Digital photography today gives us tremendous control over image contrast. It’s easy to take a flat, low-contrast scene and give it more snap. Even better, we can do something that was difficult or impossible before: photograph a high-contrast scene and retain detail in both highlights and shadows.
But even with all this control, we’re still missing the answers to some basic questions: What is my camera’s real dynamic range? Will this scene fit within that range? If so, how do I determine the right exposure? When do I need to bracket exposures and use HDR?
Luckily, there's already a framework for answering these questions: the Zone System. Ansel Adams and Fred Archer devised the Zone System in 1940 to help their students understand exposure and control contrast in their black and white negatives. With a little modification, the Zone System works just as well with digital photographs today.
Zone System Basics
The Zone System scale. Each zone is one full stop apart, with Zone 5 representing a middle tone.
The foundation of the Zone System is those mystical zones: eleven in total, numbered zero through ten. Each zone is one full stop apart. Zone 5 represents a middle tone. Anything one stop darker is Zone 4, two stops darker is Zone 3, and so on. Anything one stop lighter is Zone 6, two stops lighter is Zone 7, etc.
Zones 3 and 7 represent the limits of unprocessed files for most digital cameras. Zone 2 is too dark to show detail; essentially, it’s black. Zone 8 is too light to show good detail; it’s washed out. So Zones 3 and 7 are the lower and upper limits for retaining detail and texture.
A Simple Approach
We’ll begin with a simplified version of the Zone System that concentrates on highlights. First, you have to use manual exposure mode with the Zone System (with Auto-ISO off). Also, you must use a spot meter, and, when metering, make sure the whole spot is filled with a consistent tone; you don’t want a mixture of light and dark areas.
Start by spot-metering the most important highlight: the brightest significant part of the photograph that needs to have detail and texture. In the photograph of Yosemite’s Bridalveil Fall, I pushed my 70–200mm zoom out to 200mm and filled the camera’s central spot with the brightest part of the mist. At 100 ISO, with my aperture set at f/16, the spot-meter reading indicated 1/30 of a second. But I knew that wouldn’t work because if I used 1/30 of a second at f/16 the photograph would be underexposed. Why? Because every light meter is calibrated to a middle tone, and using an unmodified meter reading would make the mist a middle tone: Zone 5. A highlight, like the mist, should be brighter than that.
That’s actually one of the key ideas behind the Zone System: to be able to spot-meter different parts of a scene and adjust your exposure to make those elements lighter or darker, with a clear idea of how they will look in the final photograph. If you make the exposure one stop darker than your meter reading, the object at which you’re pointing your spot meter will become Zone 4; two stops darker it becomes Zone 3, and so on. Go one stop lighter than the meter reading and the object becomes Zone 6; two stops lighter, Zone 7, etc.
In this case, the sunlit mist was a highlight, so I wanted it to be lighter than a middle tone. But how much lighter? At Zone 8, the mist would be washed out. At Zone 7, the mist would be bright as a highlight should be, but with texture and detail; not washed out. Perfect.
So, with my in-camera spot meter still pointed at the brightest mist, I adjusted the shutter speed until the clouds were two stops overexposed: +2.0 on the camera’s metering scale (Figure 1, below). This “placed” the cloud on Zone 7. The resulting shutter speed was 1/8 of a second, two stops slower (and therefore brighter) than the initial meter reading of 1/30 of a second.
Figure 1 (top). I placed the brightest highlight—the sunlit mist—on Zone 7 by increasing the exposure two stops from the spot meter reading.
Figure 2 (bottom). The histogram shows the brightest pixels near, but not touching, the right edge, just where they should be.
The next step was very important: I didn’t touch anything! I’d already set the exposure, so I left the shutter speed and aperture alone, zoomed out to 70mm, re-composed, and made the photograph.
Then I checked the histogram, which looked just right (Figure 2, above). In most landscape photographs, you want the brightest pixels near, but not touching, the right edge of the histogram. In other words, you want the photograph to be as bright as possible without overexposing anything. That’s exactly what I got, without a lot of trial and error.
This same procedure works for most landscapes. Just spot meter the brightest important highlight in the scene, then use an exposure two stops lighter than the meter indicates to place the highlight on Zone 7. This will push the brightest pixels near, but not against, the right edge of the histogram. Note that you should always check the histogram and adjust the exposure if necessary.
Dynamic Range and the Zone System
As I said before, the Zone System can provide a framework for understanding and controlling contrast. Let’s start by looking at how a histogram relates to the Zone System.
The histogram on a typical DSLR shows about five Zones: Zones 3 through 7.
If we take a typical DSLR, with its Picture Style (Canon) or Picture Control (Nikon) set to its default Standard setting, the back-of-the-camera histogram shows about five Zones: Zones 3 through 7. Anything pushed up against the left edge of the histogram is Zone 2 or lower; anything pushed up against the right edge of the histogram is Zone 8 or higher.
But that histogram is based on a camera-generated JPEG, and it doesn’t represent the true dynamic range of a RAW file. RAW files actually have more usable dynamic range than that.
For example, with a RAW file from my Canon 1Ds Mark II, I can bring up detail from Zone 2 shadows. In fact, I can pull detail out of Zone 1 and even Zone 0 shadows, but there’s often too much noise for that to be useful. On the other end of the scale, I can recover detail in seemingly blown-out highlights, usually all the way up to Zone 9 (with Lightroom 4 or Adobe Camera Raw 7). This gives me seven stops of useful dynamic range, rather than the four stops shown by the camera’s histogram. Some newer cameras can do even better than that.
To test your camera’s actual, usable dynamic range, photograph an evenly-lit, textured wall. Make a series of exposures at ½ stop or ⅓ stop increments, pushing the exposures all the way up to Zone 10 (five stops brighter than the meter reading for the wall), and down to Zone 0 (five stops darker than the meter reading for the wall). Then take those images into your favourite RAW processing software. Try to recover blown-out highlights, and lighten the darkest frames to bring out texture and detail (be sure to check for noise).
You should now have a clear picture of your camera’s actual, usable dynamic range: whether you can recover highlights up to Zone 8, or 9, or even higher, and whether you can pull detail—without too much noise—out of shadows at Zone 2, or 1, or below. Armed with this knowledge, you have a framework for understanding image contrast, and can make informed decisions about exposure in the field. Let’s look at a couple of examples.
For detailed, step-by-step instructions on how to perform this dynamic range test, read this article.
Increasing Contrast: Expansion
With the photograph below of the Merced River (just outside Yosemite National Park), I metered the brightest significant highlight—the white water—and placed that on Zone 7 (Figure 3, below left). That put the darkest areas at Zone 4, so the total contrast range was about three stops.
Figure 3 (left). With the white water placed on Zone 7, the darkest shadows fell on Zone 4.
Figure 4 (right). Expanding the tonal range from four Zones to five Zones using curves.
I added contrast with the Point Curve in Lightroom 4 by adjusting the black point and white point and making an s-curve. The histogram for the final image fills most of the available space, showing that I’ve increased the contrast range from four zones (three stops) to five (four stops), with the darkest areas now at Zone 3 (Figure 4, above).
In Zone System terms, increasing contrast like this is called expansion. With a black and white negative, you increase contrast—that is, you expand the range of tones—by increasing the development of the negative. With a digital photograph, you can increase contrast by moving the black point or white point (or both), by making an s-curve, and/or by pushing a contrast slider.
Decreasing Contrast: Contraction
Decreasing contrast is called contraction. With a black and white negative you decrease contrast, or contract the range of tones, by decreasing the development of the negative. The closest digital equivalent is to take a digital negative—a RAW file—and compress the range of tones by darkening highlights, lightening shadows, or both.
In the high-contrast scene of Half Dome and the Merced River (below, left), I wasn’t concerned about the exposure for the sun as it looks natural and normal for a specular highlight like this to be blown out. So the brightest, most important highlight in this image was the cloud next to Half Dome. I spot-metered the cloud and placed it on Zone 9. That put the shadows at Zone 1 and 2 (Figure 5, below, upper right).
Figure 5 (above, upper right). With the cloud at Zone 9, the shadows fell at Zone 1 and 2, barely within the true, usable dynamic range of my camera.
Figure 6 (above, lower right). I was able to compress the tonal range from nine zones to six zones using Lightroom 4.
That’s really pushing the limits of my camera at both the high and low ends, but by using the Highlights, Shadows, and Adjustment Brush tools in Lightroom 4, I was able to take a nine-zone range and compress it to six, bringing Zone 1 up to Zone 2, Zone 2 up to Zone 3, and Zone 9 down to Zone 7 (Figure 6, above, lower right). There’s some noise in the shadows, but it’s manageable. What’s remarkable about Lightroom 4 (and Adobe Camera Raw 7) is how it accomplishes this tonal compression while keeping a natural look, and without making the midtones look flat.
Contraction Through Exposure Blending
If a scene’s contrast exceeds the camera’s true dynamic range, you can compress the range of tones by blending two or more exposures together. In this sunrise photograph from Yosemite’s Tunnel View, I spot-metered the very brightest clouds and placed them on Zone 8 (coloured highlights like this can be difficult to recover, so I didn’t want to push them to Zone 9).
I then metered the darkest part of the scene, just to the right of Bridalveil Fall. With the clouds at Zone 8, this shadow area fell to Zone 1: too dark for good, noise-free shadow detail with my camera. So I made an exposure with the clouds at Zone 8 (Figure 7), and then made an exposure one stop lighter (Figure 8, below left), and another two stops lighter (Figure 9, below center). The brightest clouds went from Zone 8 in the first exposure to Zone 9 in the second, and Zone 10 in the third. The darkest shadows went from Zone 1 in the first exposure to Zone 2, and then 3.
Figure 7 (left). First exposure, with the brightest clouds at Zone 8, and the darkest shadows at Zone 1.
Figure 8 (center). Second exposure, one stop lighter.
Figure 9 (right). Third exposure, two stops lighter.
Then, after recovering highlight detail in the darkest frame (bringing highlights down from Zone 8 to Zone 7), I took the first and third exposures and blended them together with LR/Enfuse. I like this donation-ware application because it gives more natural-looking results than HDR usually does. The blended image has good detail in both highlights and shadows, with the darkest areas at Zone 3, and the very brightest clouds at Zone 7. I completed the processing in Photoshop with considerable dodging and burning (Figure 10, below).
Figure 10. I used LR/Enfuse to blend the darkest and lightest exposures, then added dodging and burning in Photoshop. The final, blended image uses the highlights from the first exposure and the shadows from the third exposure.
The Digital Zone System
Thinking in terms of zones makes it easier to understand how the contrast of a scene relates to the dynamic range of your camera. This allows you to make informed decisions about exposure, visualize how you want to the final photograph to look, and anticipate how you might process the image. Our tools keep changing, but clear logic of the Zone System still works.
Michael Frye is a professional photographer and workshop leader specializing in landscapes and nature. He has written numerous magazine articles on the art and technique of photography and is the author or principal photographer of five print books, including The Photographer’s Guide to Yosemite and Digital Landscape Photography: In the Footsteps of Ansel Adams and the Great Masters. Magazine credits include National Wildlife, Outdoor Photographer, American Photo, Sunset, and Texas Highways, plus many others. Michael and his wife, Claudia, live in Mariposa, California, just outside Yosemite National Park. You can see more of Michael’s work on his website.