When Ansel Adams developed the Zone System with Fred Archer in 1940, he gave photographers a tool great for controlling their images—but only with black-and-white film, and only with view cameras, where sheets of film could be processed individually. Today, any photographer with a digital camera can have even more control, whether working with black-and-white or color.
Such unprecedented power creates wonderful opportunities, but also can lead to confusion. How do you apply these controls? How far should you go? Do you have to reinvent the whole photographic process? No—because while the tools may be different, the basic principles of the Zone System still apply. The Zone System gives us a vital framework for understanding and controlling contrast in our images and a path to making prints with a full, rich range of tones—the range of tones for which Adams’ photographs are so famous.
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Zone System Exposure For Digital Cameras
The Zone System requires a spot meter and full manual exposure mode. While a handheld spot meter is preferable, you can make do with your camera’s built-in spot meter mode. If you’re using the camera’s spot mode, try metering with a telephoto lens to narrow the metering coverage appropriately. The simplest approach concentrates on highlights and ignores shadows.
Start by picking the most important highlight—the brightest significant part of the scene that needs to have detail and texture. Then decide what zone that highlight should be. There are really only two choices. Zone 5 isn’t a highlight, it’s a midtone, while Zone 8 is washed out. So that leaves Zone 6 or Zone 7. Use Zone 7 for objects that are white or nearly white, like white water, snow, light sand or very light rock. Use Zone 6 for any other highlight, including tans, yellows or other pastel colors.
Next, spot-meter the highlight you’ve chosen. Make sure the whole spot is filled with a consistent tone; you don’t want a mixture of light and dark areas. To make the highlight Zone 6, increase the exposure by one stop from your meter reading. To make it Zone 7, increase the exposure by two stops. In other words, if the meter indicates 1⁄125 sec. at ƒ/16, lower the shutter speed to 1⁄60 sec. to make that highlight Zone 6 or 1⁄30 sec. to make it Zone 7. (You could change the aperture instead, of course.) Or, while pointing an in-camera spot meter at the highlight, just turn either the shutter speed or aperture dial until the exposure scale indicates one stop of overexposure (+1.0) for Zone 6 or two stops of overexposure (+2.0) for Zone 7.
|Autumn Aspens: Applying An S-Curve For Contrast. The original RAW file of these autumn aspens looked flat, but a sharp S-curve increased the contrast and brought it to life.|
The heart of the traditional Zone System is the ability to expand or contract the contrast range of the negative—to increase contrast and add impact to low-contrast images or reduce contrast to hold detail in both highlights and shadows in high-contrast scenes.
Sunset Color, Tunnel View, Yosemite: Sunrise or sunset light on mountains, or any highlight with color, should almost always be placed at Zone 6, or +1.0, with an in-camera spot meter.
With digital images, increasing contrast is easy. Use Levels or Curves to move the black and white points, and/or make an S-curve. Decreasing contrast is more difficult. While some cameras can capture a bigger dynamic range, that range is fixed and can’t be changed. But by combining exposures, it’s possible to capture detail throughout any scene, with any camera, no matter how great the contrast.
Blending Images: Exposure In The Field
To blend exposures later, you first have to capture all the necessary information in the field. Make sure the camera is on a sturdy tripod to avoid camera movement between frames. Next, use the Zone System, or any method you prefer, to get a good exposure for the highlights. Check the histogram to make sure the brightest pixels are near, but not touching, the right edge, and adjust if necessary.
Then make another exposure one stop lighter, and another, and so on, until you see space between the darkest pixels and the left edge of the histogram. You’ve then captured detail in both highlights and shadows, plus a full range of tones in between. The histograms below show what this might look like.
|Histograms For Blending Images: Histograms from four RAW images, each taken one stop apart, capturing highlights, shadows and everything in between.|
HDR Vs. Exposure Blending
Ansel Adams used reduced development to capture highlight and shadow detail in high-contrast scenes, but he was well aware that this could lead to flat, mushy areas in the midtones. The same problem confronts digital photographers when blending exposures. Too much tonal compression can reduce local contrast and produce a lifeless image. When comparing different methods of merging exposures, pay attention to those midtones and make sure they have some contrast and snap.
There are a number of software packages that help you manipulate your images using the Zone System. For example, the Ozone filter in Dfx Digital Filter software uses proprietary algorithms to divide the spectrum of the image into 11 zones, each of which can be precisely and independently adjusted. Download a free trial copy at the website: www.tiffen.com/dfx_v2_home.html.
High Dynamic Range, or HDR, uses complex algorithms to combine different exposures and capture detail in highlights and shadows. Exposure Blending takes sections of different images and fuses them together. This could be as simple as using the sky from one photograph and the foreground from another or could involve merging pieces of many images.
I find that Exposure Blending usually produces more natural-looking results than HDR and retains local contrast better, but there are exceptions, so I often try both techniques. For automated exposure blending, Photomatix’s Exposure Fusion option and L/R Enfuse are consistently excellent, but I usually can do a little better by merging the images manually in Photoshop.
Michael Frye’s latest book is Digital Landscape Photography: In the Footsteps of Ansel Adams and the Great Masters, published by Focal Press. Visit www.michaelfrye.com.