|A. Overcast days are great for shooting intimate landscapes because of the soft, uniform lighting, but present an exposure challenge when you include the sky, which is always much brighter than the land. To capture this scene of Longs Peak from Bear Lake in Rocky Mountain National Park, I spot-metered the brightest clouds and opened up three stops. That put the aspen leaves at one stop under a midtone, within range for my sensor to record adequate detail at both ends of the tonal scale.|
Sometimes your first capture is your only capture. Blow the exposure, and you’ve blown a once-in-a-lifetime opportunity. You can’t bracket high-action wildlife or outdoor sports—you’re all but guaranteed to get the wrong exposure at the decisive moment. Even landscape photographers like me need the ability to nail the exposure on the first try. I made one of my top-selling wildflower photos when the wind stopped just once during the fleeting seconds of perfect sunset light. Don’t “spray and pray,” I tell my students. Don’t turn on autobracketing, blaze away and hope for the best. Instead, I urge them, “Master the craft, and the art will follow.”
To successfully photograph a high-contrast scene with a single capture, you need two key pieces of information: What’s the dynamic range of the scene? What’s the dynamic range of your sensor? Once you have that information, you can fit the range of tones in the scene into the range your sensor can capture as well as possible.
The dynamic range of the scene is just the difference, in ƒ-stops, between the darkest important shadow and brightest important highlight. Let’s say you meter the darkest shadow and get 1/60 sec. at ƒ/2.8. (In other words, you fill the frame with the darkest shadow—nothing else—and your camera recommends an exposure of 1/60 sec. at ƒ/2.8.) You meter the brightest highlight and get 1/60 sec. at ƒ/22. The dynamic range is six stops. (Count up from ƒ/2.8 in full-stop increments: ƒ/4, ƒ/5.6, ƒ/8, ƒ/11, ƒ/16, ƒ/22.) If you expose the scene at 1/60 sec. at ƒ/8 (midway between the shadow and highlight readings), then every part of the scene that meters 1⁄60 sec. at ƒ/8 will be rendered as a midtone. The darkest shadows will be three stops darker than midtone, and the brightest highlights will be three stops brighter than midtone.
The best tool for measuring the dynamic range of a scene is a handheld spot meter. It allows you to mount your camera on a tripod and compose precisely, then leave your camera locked down while you meter the scene and calculate the exposure. My Sekonic L-608 spot meter also lets me memorize the exposure for any part of the scene, such as the darkest shadow. The meter then reads out the difference, in stops, between the memorized value and the value of whatever I meter next, such as the brightest highlights. That makes it effortless to measure a scene’s dynamic range.
If you don’t have a handheld meter, use your in-camera spot meter, coupled with manual exposure mode. Almost all DSLRs will display an analog exposure scale when placed in manual-exposure mode. Point the spot meter at a part of the scene you want to render as a midtone. Green grass and medium-gray rocks often are good starting points. Adjust the exposure until the pointer is in the middle of the analog scale, indicating a “correct” (meaning midtone) exposure for that part of the scene. Now point the spot meter at the darkest important shadow. Don’t adjust the shutter speed or aperture. The pointer will move down the analog scale and tell you, in stops, how much darker than midtone that part of the scene will be. Now point the spot meter at the highlights and see how much brighter than midtone they are. If need be, switch to a telephoto to get a narrower angle of view for your spot meter.
Some analog exposure scales only extend +2 or -2 stops from midtone. If the dynamic range exceeds that, you’ll need a different approach. Start by pointing the spot meter at the shadow and setting the “correct” exposure. The pointer will be in the middle of the analog scale. (This isn’t the exposure you’ll actually use to make the picture.) Then point the meter at the highlight, reset the “correct” exposure and calculate the difference. To avoid the mental math, you can count clicks as you adjust the aperture and/or shutter speed. Each click will represent a change of a 1/3- or ½-stop, depending on the settings you’ve chosen in your camera’s menus. If it takes 18 clicks, each representing a 1/3-stop, to go from the correct exposure for the shadows to the correct exposure for the highlights, then the range is 6 stops. It’s usually easiest to adjust shutter speed alone, since its range is much wider than the aperture range.
If you have a quick-release tripod head, you can compose your shot, lock down the tripod controls, remove the camera from the tripod head, meter the scene and reattach the camera without disturbing your composition.
Knowing the dynamic range of a scene is meaningless unless you also know how wide a range your sensor can capture. Unfortunately, camera manufacturers rarely publish a number, which means most photographers don’t know the dynamic range of their sensor—but should. In the days when nearly all outdoor photographers shot transparency film, the dynamic range of the capture medium was essentially fixed. If you were shooting Velvia, for example, you knew you had a range of about 5 stops. You could place the brightest important highlights 2.3 stops brighter than a midtone and expect bright white highlights with barely printable detail. If you placed the darkest important shadows at 2.7 stops darker than midtone, you would get dark shadows just shy of pure black.
Unlike film, the dynamic range of sensors isn’t a fixed, known quantity. In fact, it varies from camera to camera. Older, less expensive DSLRs might have a range of six stops. Newer and more expensive models usually have a greater dynamic range, as do cameras with larger sensors—perhaps as much as nine stops. The only way to determine that range accurately is by performing a simple test. In brief, it involves selecting near-white and near-black subjects and making a series of bracketed exposures, then examining the images in a RAW converter to determine the sensor’s ability to hold detail in progressively lighter and darker captures. (See the sidebar for full details.) For my Canon EOS-1Ds Mark III, I measure a range from +4 stops to -5 stops at the extreme limit, from near-white to near-black. Further testing showed I could hold reasonable color and detail over a range of about four stops (+2 to -2).
Armed with this information, I can approach high-contrast scenes with confidence. Last fall, for example, I photographed Longs Peak in Colorado framed by colorful aspen. Using a split-neutral-density filter, either virtual or physical, to tame the bright sky would have rendered the tops of the trees too dark. The fluttering leaves made HDR techniques unworkable. But my testing had showed I could spot-meter the bright gray clouds and place them three stops over a midtone. In other words, I could meter the clouds at 1/30 sec. at ƒ/16, let’s say, then open up three stops to ¼ sec. at ƒ/16. I then metered the leaves at 1½ sec. at ƒ/16, or one stop darker than the exposure I actually used (¼ sec. at ƒ/16). The final exposure gave me light gray clouds in my digital file and excellent detail in the leaves. When a shaft of sunrise light found an unexpected hole in the clouds and spotlighted the leaves, I was ready.
Don’t assume that you can just average the shadow and highlight readings and blaze away. Let’s say you meter some shadowed flowers and sunlit mountains and determine that you have a five-stop range—within the range of almost any DSLR. “Eureka!” you think. I’ll just pick an exposure in the middle of the range and it will be perfect.
Wrong! Flowers (or at least the green foliage around them) need to be exposed close to a midtone density to look right in a print. If you choose an exposure in the middle of that five-stop range, your flowers will be 2½ stops darker than midtone, and your highlights will be 2½ stops brighter, giving you very dark, muddy flowers and washed-out peaks. If you expose the flowers as a midtone, as you should, that puts the highlights 5 stops brighter than midtone—well beyond the range of even the best DSLRs. The solution in this case almost always will be a physical or virtual split-ND filter or some variation of HDR technique.
As this example shows, your exposure strategy needs to consider the proper density for the various elements in your scene, as well as the dynamic range of the scene and your sensor. But the starting point always is this: If you know both your sensor’s and your scene’s dynamic range, you can place the brightest important highlights just below your sensor’s limit. That, in turn, will give you the best shadow detail possible in a single capture that also preserves the highlights. And if the scene won’t fit gracefully inside your sensor’s dynamic range, you’ll learn that in the field when there’s still time to do something about it.
To measure your sensor’s dynamic range, start by selecting near-white and near-black subjects that have some variation in tone. I chose a piece of dirty-white deck furniture and a dark shadow beneath that furniture. Now make a series of bracketed exposures of each subject.
For the near-white subject, start with the exposure the camera recommends when you fill the frame with the subject and open up a 1/3-stop for each successive frame by adjusting the shutter speed in manual-exposure mode. Your final frame should be 5 stops overexposed. For the near-black subject, start with the exposure the camera recommends and close down a 1/3-stop for each successive frame. Your final frame should be 5 stops underexposed.
Examine the photos in a RAW converter (I used Adobe Camera Raw). I adjusted the Exposure, Recovery and Fill Light sliders as necessary to get the best possible detail. As you examine lighter and lighter exposures, you’ll eventually find one where you can’t recover printable detail no matter what you do. This is the point where your sensor has saturated. As you examine darker and darker exposures, you’ll eventually find one where you can’t recover printable detail without generating unacceptable noise. This is the lower limit to your camera’s ability to hold shadow detail. For my Canon EOS-1Ds Mark III, I measured a range from +4 stops to -5 stops at the extreme limit, from near-white to near-black.
In addition to knowing the outer limits of your sensor, it’s also important to know the range with reasonable color and detail. To test this admittedly subjective parameter, I photographed some flowers, bracketing +3 and -3 stops in 1/3-stop increments. I used Camera Raw to adjust each exposure to match, as closely as possible, the middle exposure in the set (the one shot at the camera’s recommendation, which proved to be correct). That testing showed I could hold adequate color and detail over a range of about four stops (+2 to -2). Images overexposed more than two stops remained pale and washed out no matter what I did. Images underexposed more than two stops became muddy with excessive noise when I tried to bring them close to midtone.
While it’s always best to expose a midtoned part of a scene as a midtone in the original capture, this second test showed I could hold decent color in parts of the subject exposed within a range of +2 or -2 stops from the meter’s recommendation.
For more information and to see more of Glenn Randall’s photography, visit www.glennrandall.com.