|Blue Lake At Sunrise, Mount Sneffels Wilderness, San Juan Mountains, Colorado. Randall used the Rembrandt Solution to get this image. He stacked a photo exposed properly for highlights and one exposed properly for shadows, and combined the two in the computer.|
Menacing gray clouds filled the sky when I arrived before dawn on the crest of Black Face in the San Juan Mountains near Telluride, Colorado. I had wagered a good night's sleep on this sunrise, but my decision to get up at 2 a.m. and hike two and a half hours in the dark looked like a gamble I had lost. Minutes later, however, the clouds to the east began to tear apart, revealing ragged holes rim-lit with golden light from the rising sun. The scene was spectacular, but with both backlit clouds and deeply shadowed, forested valleys in the frame, the contrast was high.
Black Face, Lizard Head Wilderness, San Juan Mountains, Colorado. As described in the article, Randall used HDR software after the fact to create this image from a series of bracketed frames of the rapidly changing scene.
What exposure strategy should I use? There was no time for painstaking calculations. Rather than spot-metering frantically, I resorted to the "Universal Exposure Strategy." To understand that strategy, you need some background. In my view, there are four basic exposure strategies for landscape photography. As I'll explain in more detail, the four strategies are: PhD, Limiting Factor, Rembrandt Solution and HDR. In an ideal world, photographers would always have the leisure to carefully analyze which exposure strategy would give them the perfect result. But the world is imperfect, and the most promising situations are often fleeting.
When I'm rushed, and nothing is moving within the frame (the big caveat), I often resort to the Universal Exposure Strategy. I set the camera to give me a five-frame bracket set with a one-stop bracket interval. With that strategy, I can come away from the shoot confident that I have the data to choose, after the fact, whichever basic exposure strategy will give me the best result.
Let's investigate the four basic exposure strategies more deeply.
1 PhD No, you don't need a doctorate. PhD stands for Push here, Dummy. If you're shooting a midtone subject in soft, even lighting, your camera will give you the right exposure time after time. The most common PhD situation is an intimate landscape of wildflowers on an overcast day. With no sky in the frame, the meter reads primarily off the green foliage, which is a classic midtone subject. The entire sky is the light source. Such a broad source gives you low-contrast lighting. You can forget about exposure and concentrate on composition.
2 Limiting Factor This is the best exposure strategy to use in slightly higher contrast situations. The limiting factor is the highlights: Don't blow them out! The simplest procedure is to shoot a test frame at the exposure recommended by the camera's meter, then check the histogram.
The mound of data on the right side that represents the highlights should be almost, but not quite, butted up against the right side of the graph. If it's too far to the left, increase exposure a bit and try again.
If the mound of data is cut off by the right side of the graph, reduce exposure and try again. If your camera gives you a histogram with exposure simulation in Live View, you can adjust exposure before shooting until the highlights are almost, but not quite, clipped.
The most sophisticated way to use the Limiting Factor strategy is to spot-meter the highlights and open up an appropriate number of stops to place them just below clipping. To use this technique effectively, you need to know the dynamic range of your sensor, which you can establish by testing. I know, for example, that with my Canon EOS-1Ds Mark III, I can spot-meter a bright white cloud, open up three stops and still hold printable detail.
Aspen Panorama, Colorado Trail, San Isabel National Forest, Colorado. Randall used the Limiting Factor strategy to shoot a series of images that were stitched together to make the panorama.
3 Rembrandt Solution As contrast increases still further, it may be impossible to capture all the detail you want in both highlights and shadows in a single frame. My solution is a digital "graduated neutral-density" technique I call the Rembrandt Solution since it uses visual principles pioneered by the famed portrait painter.
I start by shooting two frames, one exposed for highlights, one for shadows. Next, I stack the two frames on top of each other in either Photoshop or Photoshop Elements (version 9 or later), with the dark (good highlights) frame on top. I add a layer mask to the top layer, then draw a white-to-black gradient on the mask to merge the two frames in a way that's exactly analogous, in terms of the end result, to using a physical, grad neutral-density filter in the field. For more details, see "The Rembrandt Solution" (Outdoor Photographer, September 2009).
4 HDR As a last resort, in the highest contrast situations, you may be forced to rely on HDR techniques to merge several bracketed frames in tone-mapping software. At a minimum, you'll need three frames shot at -2, 0 and +2 exposure compensation using the auto-bracketing feature on your camera. There are many good HDR programs, but my favorites continue to be HDRsoft Photomatix and Nik Software HDR Efex Pro.
The Universal Exposure Strategy lets you choose, after the fact, which of the four basic exposure strategies to employ. In a PhD situation, the middle frame of the bracketed set should be perfect. In fact, if you're completely confident it's a PhD scene, you don't need to bracket at all.
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.
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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