Tuesday, June 21, 2011
The Rarest Light
Look for the gap and the glow, and you’ll find light that transforms a scene into something extraordinary
Now let's take a look at the atmospheric optics of "glow" photos, where a large bank of clouds lights up with such strong and colorful light that the clouds themselves become the dominant light source. First, consider what happens on a completely clear morning. When the sun is below the horizon, the blue sky is actually the dominant light source. Photographs taken under this lighting usually have inadequate contrast and a somber, cool cast. Photographs taken precisely at the moment of sunrise have a warm tone, with moderate contrast, but within a few minutes the contrast has strengthened dramatically, often too much so, and the light is basically white.
Glow photos, on the other hand, are warm in tone with soft, but not flat contrast. The part of our visual system that sees depth and dimension is color-blind. It works strictly on luminance values, or differences in brightness. In effect, it's a black-and-white system, which is why shadows are your friends, giving your images dimension and depth, and why both frontlit photos and those taken before sunrise and after sunset on clear days (when the lighting is all shadow) can appear flat. Glow photos hit the perfect balance—enough contrast in the land to reveal form, but not so much contrast that your sensor has trouble straddling the difference in light intensities between highlights and shadows.
Exposure for the land portion of glow photos is easy, since the lighting is soft. The sky can be very bright, however, particularly if the glowing clouds are in the frame. One solution is to spot-meter the sky, then place the brightest part of the sky as high in the tonal scale as you can without clipping the highlights.
Where To Find Gap And Glow Light
Glow photos can occur almost anywhere. I've even seen a perceptible mauve glow in the depths of Colorado's aptly named Black Canyon of the Gunnison. All that's required is a sufficiently large bank of clouds that light up brightly enough to overpower the light from the blue sky and shadowed blue-gray clouds, therefore becoming the dominant light source.
To take full advantage of a gap situation, you need a subject to receive the light. In the mountains, look for peaks that will receive unobstructed sunrise or sunset light, either because the peaks rise above the plains, as described earlier, or because the peaks rise at the head of valleys that face the rising or setting sun. A foreground can only receive moment-of-sunrise light if the horizon is at the same elevation or lower. The Photographer's Ephemeris (photoephemeris.com) can help you find both kinds of locations by showing you the angle of sunrise and sunset at different times of year, as well as the elevations of obstacles that can block sunrise or sunset light.
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