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Tuesday, February 12, 2013

The Universal Exposure Strategy

How to harness the power within your camera and your eye to get perfect exposures for every kind of lighting situation

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Here's an example. Let's say I spot-meter the shadowed foreground foliage at 1⁄4 sec., ƒ/16. I set that exposure on the camera in manual-exposure mode. Next, I spot-meter the bright mountains and get 1⁄30 sec., ƒ/16—a three-stop difference. My first exposure will render the foreground flowers perfectly, but place the background mountains three stops over midtone, which makes them pale and washed out. I want to place them about one stop over midtone. They're a highlight, after all, so they should be a little brighter than midtone. One stop over midtone is two stops darker than they will be rendered in the first frame, so I set my auto-bracketing interval to two stops and fire away. The first frame will be exposed at 1⁄4 sec., ƒ/16, giving me perfect flowers, and the second will be two stops darker at 1⁄15 sec., ƒ/16, giving me perfect mountains.

This complicated procedure is only necessary if something is moving within the frame. If not, I use the Universal Exposure Strategy. But, what if your camera limits you to a three-frame bracket set? Here's a tip for efficiently shooting a five-frame bracket with a camera that only will do a three-frame bracket at one time:

Set bracketing to three frames with a one-stop bracket interval.
Set exposure compensation to +1.
Shoot three frames, which will give you the series 0 exposure compensation, +1 and +2.
Now set the exposure compensation to -1 and shoot three frames.

That gives you the sequence -2, -1 and 0 (again). You'll have one duplicate frame (the metered exposure, 0 exposure compensation). Discard the duplicate, and you have a five-frame bracket set with a one-stop bracket interval.

When I returned home from my shoot, I experimented with different approaches to processing my five-frame bracketed sets. I finally resorted to Photomatix, with further processing in Photoshop, to produce the result I wanted. By employing the Universal Exposure Strategy, I had the freedom to choose, after the fact, whichever exposure strategy gave me the ideal rendering of an amazing sunrise I never expected to see.

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