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Nuts & Bolts
A recent column comparing raw files to jpegs generated a fair amount of correspondence, not about the advantages of one form over the other, but how to deal with the limited exposure latitude of jpegs and the limitations of a camera's reflected light, automatic TTL metering.
Newspaper photographers are often locked into the jpeg format where speed of delivery is essential, especially if they are going to transmit their pictures back to the paper. They face a situation not unlike the photographers who first shot color for the newsmagazines. The photographers were used to black-and-white negative films rich in exposure latitude. Suddenly they were using color slide films with very limited exposure latitude and the ability to capture a brightness range of 4 to 5 stops. There isn't that much difference between that situation and newspaper photographers moving from latitude-rich color negative films to the limitation of digital photography's jpegs. And many of the solutions that the film photographers came up with work perfectly well for the digital photographer.
The first solution: bracket your exposures. "I can't do that. What if THE frame isn't properly exposed?" Give me a break. Outside of sports and riots there isn't too much that can't be done by initially shooting at what you feel is the correct exposure and following up with a bracket for insurance purposes. If war photographers can do it, you can add a bracket to your coverage of a City Hall meeting, especially since auto bracketing is built into so many of today's digital cameras.
Ninety percent of the time, my own technique with a camera that auto brackets is to bracket every jpeg. I take a picture at the moment that I think is appropriate. The camera then rapidly adds a frame with more exposure and a frame with less exposure. These added frames are not taken at the precise moment that I deemed the perfect moment. Although it does not say much for a lifetime devoted to capturing the exact moment of truth, the bracketed frames are often just as good, occasionally save my tail and often provide a dramatic interpretation of the scene that through-the-lens auto exposure did not.
The second solution: the hand-held, incident meter. The incident meter, that small box with the half a ping-pong ball attached, measures the light falling on the subject, not the light reflected off of it. It first made its appearance in Hollywood where, unlike the reflected light meter (whose close-up reading renders whatever tone it reads a medium gray) the incident meter reads the intensity of the light falling on the subject and guarantees that the virginal, pale ingénue remains pale and the tanned, manly hero remains deeply tanned and manly.
It also responds more to the key or main light than the shadow areas. Color slide film and digital photography share the inability to deal with an overexposed highlight. With slide film, the highlight is reduced to unreclaimable, clear cellophane. With the digital image, the highlight is somewhere off the histogram in digital cellophane land. This is true of both raw files and jpegs. Incident readings tend to protect you from this.
Because it responds more to the keylight than the shadows and is not mislead by backlight and bright or dark backgrounds, the incident meter became a very popular meter with photojournalists using slide film and, if folks I've been speaking to are any indication, it's gaining in popularity with jpeg shooters. It does a great job with close-ups and medium shots where identifiable values like flesh tones are a significant part of the image. (Bracketing and reflected light TTL still work better for aerial photography, stained glass windows and riots shot at a distance.)
Because the transmission, or t-stop, of many elemented zoom lenses can be significantly different from the f-stop that is calculated from the lens' focal length and the aperture's diameter, I use an Expo Disc rather than a hand-held, incident meter http://www.expodisc.com. This is an opalescent disc whose color and light transmission are carefully controlled so that shooting with it placed in front of the lens produces a frame similar to the one you would get by shooting an 18 percent gray card. But the Expo Disc is a lot smaller and a lot more convenient way to determine incident exposure and color balance than by carrying a gray card.
Although these days the Expo Disc is primarily used to establish correct, customized color balance settings in a variety of situations, it was originally (in the days of film) used to provide a simple way to take incident readings with a TTL metered camera. Although there are a variety of ways you can use the Expo Disc to determine exposure, I simply hold it in front of my camera lens, point the camera from subject position towards where the camera will be (or a position where the light is similar) and fire a shot on automatic exposure. I then transfer that exposure value to manual settings on the camera.
If that manually set incident exposure reading is significantly different from the TTL reading, I ask myself why. If I'm shooting a coal pit or snowscape or under very contrasty harsh lighting, I split the difference between the two meters; neither is very good in those situations. But most of the time, if the TTL exposure is just bouncing a fraction of a stop to either side of the manually set incident exposure, I stick with the incident and get a more consistent result than a series with the camera on automatic TTL where a change in framing, not a change in subject brightness, produces a variety of exposures.
The third solution: the histogram. Obviously the best way to check exposure with a digital camera is to check the histogram. Unfortunately, it is almost impossible to do in bright sunlight, takes significantly longer time than either bracketing or a quick incident reading and requires some experience to evaluate anything beyond values that sit happily in the middle of the histogram's range. But, if you can do it, do it and learn to do it well. It's the best way; it's the digital way. It's just not going to work walking backwards in front of the celebrity exiting the courthouse. That will still remain the province of auto exposure, perhaps a touch of auto bracketing, and intense, deeply felt auto prayer.
Of course, you can also set your camera to shoot both raw files and jpegs, just in case, and fall back on processing and correcting raw files if all else fails. While the advertised four-stop range of raw files is a bit exaggerated and they can take a fair amount of deadline-delaying time to process, on occasion raw files can save your butt. And, if not, they can produce really nice prints for contests.
© Bill Pierce
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