Fog and Backlighting for Mood in Photographs

Sunlight from behind a subject combined with fog can have a dramatic effect on photographs, often producing a rich, saturated setting of golden light. A low sun angle and presence of sufficient moisture in the air are the key ingredients for this effect.

Sun angle is the more predictable of the two. Sometimes, simple observation of an area the day before is all that’s required. Computer programs are available for such a calculation, but typically assume a featureless horizon. Mountains, trees, and other features that may block the light complicate the calculations. Also keep in mind that determination of the right time for one area does not necessarily apply to other areas, even those in close proximity. I once spent over an hour on a -20 F/-29 C day waiting (mostly in a car) for the sun to clear the mountains and provide the light that I had envisioned.

Capturing visible moisture in the air is not as easy as figuring out sun angles. Fog is formed when the air temperature has dropped below the dew point and small droplets of water are suspended in the air. Rain creates droplets too large to produce this effect. Air cools to produce fog in a number of different ways; the five different types of fog are named by the manner in which they were formed. Radiation and advection are the most common.

Radiation Fog

Fog formed under clear, calm skies when infrared heat escapes to the upper atmosphere and the air is cooled to its dew point is radiation fog. This is also known as ground fog and is the most common type of fog over land. Autumn tends to be the best time of year for it.

Radiation fog is the most predictable in my area and most useful for me since I spend most of my time photographing wildlife. As summer draws to a close, a cold, clear, calm night will almost certainly provide good ground fog in low lying areas. Such conditions occur most frequently when a high pressure system is dominant over the area. If I anticipate having time to take advantage of the situation, I will scout an area looking for moose, which are common in my area and frequent low-lying terrain. With forecasts and some luck I’ll have nice ground fog in the morning; the sun will not be obscured by higher clouds; and the moose will have positioned themselves for good photographic opportunities.

Advection Fog

Advection fog occurs when warm, humid air is cooled to its dew point by its contact with a cooler surface below, such as snow, ice, and cold water. Examples of this fog include that seen on the Pacific Coast as well as the west coast of the United Kingdom.

Steam Fog

Steam fog occurs when cooler air rests above warmer water and vapor that evaporates into the air cools to its dew point. This type of fog can be seen over bodies of water in fall and winter when cold, dry air passes over warmer water. It may also be seen over wet surfaces following rainfall.

Upslope Fog

When air is forced to rise up a large slope and cools to its dew point, upslope fog is formed. This effect promotes lush vegetation on the windward side of many islands since the moisture frequently forms large enough droplets to fall as rain or snow.

Frontal Fog

When rain drops fall into dry, cooler air below, frontal fog is formed. As the drops evaporate, water vapor is introduced into the cooler air. Very quickly, the vapor condenses into small fog droplets.

Exposure

The very nature of backlighting often provides exposure ranges outside the limitations of film or sensor. Consequently, you may need to decide whether to lose details in the light areas or the dark areas of your image. Bracketing your exposure can be very useful in obtaining at least a few images that capture your vision. The amount of exposure compensation is dependent upon metering mode; I frequently bracket up to plus and minus two stops after metering off a mid-toned object in the scene.

Combining backlighting and fog can be a matter of foresight and planning, or just plain good luck. Done successfully, these types of images can add dramatic flair to your image collection.

The US Naval Observatory offers a variety of products useful to photographers interested in solar and lunar data. http://www.usno.navy.mil

This program allows for differences in elevation. http://www.susdesign.com/sunangle/