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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

This Article Features Photo Zoom

Cow Parsnip And Aspen, Sneffels Highline Trail, San Juan Mountains, Colorado. The soft lighting conditions called for the PhD approach, which lets your camera do all of the thinking.
In a Limiting Factor situation, you always get your choice of the ideal exposure because you use a one-stop bracket interval instead of two. If you bracket with a two-stop interval, as is often recommended for HDR, you risk straddling the ideal exposure. One bracketed frame may be too dark, but the next frame in the set may be too light. The difference in exposure between frames is too great.

Similarly, the Universal Exposure Strategy lets you choose the ideal two frames for the Rembrandt Solution. Of course, if you choose HDR, you can use all five frames in your favorite HDR software.

The big caveat is that nothing can be moving within the frame. If you're shooting a grand landscape with flowers in the shade and sunset light on the peaks above, for example, you want the first frame of your bracketed set to be the ideal exposure for the flowers. You can then wait for the instant when the wind truly stops and fire away, confident that your first frame will have razor-sharp petals with just the right density.

If you try to shoot a five-frame bracketed set, your first exposure will attempt to straddle the difference between the dark flowers and sunlit peaks and probably render neither subject satisfactorily. By the time the camera gets around to making the frame with correctly exposed flowers, the wind may be blowing again.

In that situation, I generally rely on the Rembrandt Solution to produce the final image, but I change my exposure strategy. I start by spot-metering the green foliage around the flowers and setting that as my base exposure in manual exposure mode.

My first frame, therefore, will give me perfect flowers. Next, I calculate how much less exposure the bright background needs. I set the bracket interval to that value so my second exposure will give me perfect mountains. I set the camera for a two-frame bracket set and the bracket order at zero, minus, plus and then fire away when the wind stops. Then I stack the two exposures in Photoshop as described and merge them using a gradient on a layer mask.

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