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Tuesday, February 9, 2010

The Digital Zone System

If you thought DSLRs and new technology made the Zone System obsolete, think again. Updating the classic Ansel Adams tool for proper exposure will make your digital photographs as good as they can be.

This Article Features Photo Zoom

Zones And Histograms:

This diagram shows approximately how each zone relates to a histogram. The spike at the right-hand edge of this histogram indicates pixels that are overexposed —Zone 8 or higher. Anything at the far-left edge of the histogram is Zone 2 or lower—black. In landscape photographs, highlights are vital. Usually, the brightest pixels should be near, but not touching, the right edge of the histogram.
Controlling Contrast
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.


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