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Friday, August 1, 2008

In Praise Of Pea Soup


When you feel the cool dampness of fog starting to roll in, pull out your camera and get ready for a rare opportunity

The final and probably rarest of the big three fog types is upslope fog. This occurs when moist, stable air is forced up to a higher altitude by the terrain, a high hill, cliff or mountain, and is cooled to the dew point by the lower temperatures up there. The most dramatic place I’ve seen this occur is on Table Mountain above Cape Town, South Africa. There, because the top of the mountain is flat, the fog overflows the plateau and pours back down the slope, looking like a cascade of heavy cream flowing down the side of the mountain. But usually, upslope fog just fills in the valleys first and doesn’t “pour” like the Table Mountain phenomenon.

The bottom line on predicting fog? When I come across calm winds, clear skies, moist air and overnight lows that meet or drop below the dew point, I’m on fog alert. Before the advent of the Internet, I always carried one of those small, battery-powered weather-band radios that play continuous, updated forecasts from local offices of NOAA (National Oceanic and Atmospheric Administration) on domestic assignment. They’re still excellent investments (and you don’t need to have Internet access, just batteries and the right radio), but often the weather maps and resources of the Internet are more detailed.

Shooting The Soup. Once you find yourself in a fog, you’re still not out of the woods; there are a few pitfalls to avoid. Fog can be highly reflective and can cause a bit of underexposure, resulting in muddy, gray images. This was much more of a problem in the film era than it seems to be in digital, but careful metering can help you capture the delicateness of some fogs.

If I were writing this even five or six years ago, I’d say that in heavy fog, conditions start out with an exposure compensation of about +1 stop. But with our onboard histograms ever at the ready, I always start out just doing what the camera meter tells me. A quick look at the histogram tells me if my exposure is within the boundaries of the chip’s sensitivity. I’m especially careful not to burn out or clip any of the highlights (which can be plentiful in fog). So my method is to shoot, consult the histogram and make any necessary adjustments.

When you have a thick fog—one of those coastal advection blankets—the light can get dull and gray. Here’s where I might play with the camera’s white balance a bit. Try shooting some heavy fog in Tungsten white balance instead of Daylight. Now all that gray goes blue, and it picks up a moody twilight feel even if you’ve missed twilight by an hour or two—and it looks perfectly natural.

Of course, there are ways to simulate fog. Old-fashioned glass fog filters can do a credible job, but the results can look more like low-contrast diffusion than actual atmospheric fog. Software programs like Nik Color Efex have fog filters that can be applied after the fact in Photoshop. These look surprisingly good, especially since you can fine-tune the intensity and “graduation” of the fog. Most of my clients won’t accept photographs that are altered after the fact, so I don’t take the opportunity to use the software approach much. When I have for personal prints, though, it has worked well.

And then there’s the old low-tech, automatic human fog machine approach. Breathe on the front element of your lens (or, preferably, the protective filter over the front element of your lens), and shoot as the condensation clears! It’s a crude and unpredictable re-creation of one of nature’s most prized shooting conditions, but when you’d like to be in a fog, and you aren’t, it can save the day!

For a schedule of Bob Krist’s workshops and seminars, check his website, www.bobkrist.com, under the “Teach and Talk” heading.

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