Rainbows are one of the most magical of sky effects, elusive, mysterious and colorful. They’re a natural subject for the nature photographer, so much so that they do run the risk of cliche, but they can also can put the final “shazam” on what would already be an interesting image. With a few simple hints and techniques, you’ll gain a better understanding of how to capture and convey their magic.
The first challenge in finding a rainbow is finding one to photograph in the first place. Any rainbow requires two elements, light and water droplets. The light needs to be from small source and very bright, so it’ll usually need to be direct sunlight (although it is possible to find and photograph “moonbows”) they’re very hard to see and even harder to capture well. The need for both sunlight and rain or mist means you’ll usually need to look for rainbows in mixed weather (rainy conditions without complete overcast) or in other places where mists form in broad sunlight (waterfalls, such as my Iceland image above, geysers, and the like.)
The physics of rainbows shows that when they appear, primary rainbows will always appear at angles about 140 degrees from the sun, in other words, you’ll want to look for rainbows not so much toward the sun as away from it. This figure has one important implication for nature photographers, unless you can see down for a long way (into a deep canyon, or down from a mountaintop or airplane) you won’t be able to see a rainbow in the sky when the sun is high. At moderate latitudes, your chances for rainbows will be limited to the beginning and end of the day. As you move closer to the poles, the sun stays low longer (if there’s sun at all!), and opportunities increase.
Because rainbows aren’t physical objects but reflections from water droplets, it is possible at times to “move the rainbow”, as you move your point of view, the rainbow appears to move relative to the objects in front of and behind it, so long as there is in fact a rainbow visible from the new location. In some situations this will allow you to move the rainbow within the composition, perhaps for the better.
Bringing out the subjective intensity of rainbows seems to require care, all too often snapshots of rainbows lack the punch they seem to have in person. Polarizers (turned correctly) will help here, almost doubling the intensity of the rainbow relative to the scene around it, and are a great place to start. Proper exposure is also critical, as the most saturated rainbow colors will occur if the rainbow is exposed for the midtones, too light or too dark and the colors will muddy up or fade.
One final bit of advice, it is all too easy when one sees a great-looking rainbow to try and photograph it alone, for it’s own sake. While you’ll be able to get some pretty snapshots that way, in general those images rarely seem “great” when you’re done with them. Instead, look to combine rainbows with other elements of the scene, whether as a wide landscape, or as a more abstracted detail shot such as the one at the top of this article, you’ll find those images have a greater potential to really sing.