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

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Morning fog slowly burns off in Tuscany, Italy.

Any landscape photographer who prays and waits for conditions that lower contrast, decrease saturation, obscure sharpness and ruin resolution might be considered to be a couple of sandwiches short of a picnic, a real madman. Yet, when that condition is fog, there’s a definite method to that madness.

Nothing can add a sense of moment, mystery and beauty to a landscape like those beautiful wisps of water vapor we know as fog. It’s an elusive and hard-to-predict condition, and most of us consider ourselves lucky when we stumble upon it. Yet, like most things, the more you know about it, the less mysterious it becomes, and the better your chances are of getting “lucky.” So let’s look at “the pea soup,” why and when it happens and some of the pitfalls of trying to photograph in it.

What’s The Soup Of The Day? It’s important to realize that there are at least three major types of fog: radiation, advection and upslope. Radiation fog is my personal favorite because it occurs during times of calm winds and clear skies, when the temperature and dew point get close to one another.

Dew point, according to, is defined as: “The temperature at which the water vapor contained in a volume of air at a given atmospheric pressure reaches saturation.” The dew point varies, depending on how much water vapor the air contains, with humid air having a higher dew point than dry air. When large droplets of condensation form, they’re deposited onto surfaces as dew. When smaller droplets form, they remain suspended in the air as mist or fog—lovely, lovely fog.

Radiation fog occurs because the clear skies allow the land to radiate heat freely, cooling the air near the surface to the dew point and causing fog to appear. This usually happens in the early morning or evening, when the light is sweet. Radiation fog is usually patchy; that’s to say it doesn’t blanket huge areas evenly. In morning conditions, as the sun rises, the temperature rises and burns off the fog. So you get those great conditions with shafts of sunlight penetrating the fog, which looks especially good in backlight.

I’ve run into radiation fog most often in the fall and the spring. When I was looking to shoot aerials for my coffee-table book about Bucks County, Pennsylvania, I watched the dew point closely until a clear night when it looked like the temperature and the dew point would meet up. Sure enough, there was wispy fog over the Delaware River and among the stands of beautiful fall foliage in the valleys. In Tuscany, Italy, the springs are humid and clear, and there’s often a morning fog that’s well worth skipping your morning cappuccino to photograph. (You always can get your caffeine later, after the fog has burned off!)

Advection fog occurs most often near the coast, when moist air moves in from over the water to over the land. The moist air condenses into fog when cooled by the land. This is the type of fog that occurs off the Maine coast and other seaside areas. Tough to predict, you need to know wind direction and surface temperatures along the shores, water and land. A high relative humidity also is a necessity.

I never got the hang of predicting this condition myself, but fortunately, the weatherpersons are really good at it, especially along those coasts where it’s a common occurrence. If you hear of 100 percent humidity in a nearby area and there are winds moving in your direction, you’re likely to experience a nice dose of advection fog that can last for days. It’s thicker and more persistent than radiation fog, but can be dramatic.

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,, under the “Teach and Talk” heading.

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