A rainbow is arguably the most beautiful optical light effect created by sunlight. It is formed by millions of raindrops that break the sunlight into different colors. Shooting a rainbow is fairly easy, but there are some nice things to know about.
Rainbows take many forms. There are multiple bows, bows that cross, red bows, twinned bows, colored fringes, dark bands, spokes, and more. For a rainbow you need two things; sunshine and falling rain. The raindrops break the sunlight in different wave lengths, each having its own characteristic color. A rainbow will always show the colors red, orange, yellow, green, blue, and violet, as seen from top to bottom. A rainbow always appears opposite to the sun, which means you will have the sunlight coming from behind. Therefore you will often have the risk of capturing your own shadow, especially when the sun is low on the horizon and shadows are very long.
A rainbow may seems very common, but in reality it is not. At any given location, there are less than ten rainbows in a year. Halos around the sun are much more frequent.
How the rainbow will appear depends on how high the sun is above the horizon. The closer to the horizon, the higher the bow will appear in the sky. But also when the sun is high in de the sky, a rainbow may be visible low at the horizon. From a high vintage point, it might be possible to see not only a bow, but an almost complete circle. This can be witnessed on a high mountain peak, or from an airplane.
Because of the dark clouds behind a rainbow, heavy with raindrops, the colors will stand out very well. Foreground can even be lit by the sun, making a wonderful contrast with beautiful light. You may even see streaks of falling rain in the sky.
A rainbow is not just an arc of colored rings. In reality it is a shining disk that is brightened very strongly towards the rim. That is why the sky is always brighter inside the bow, something that is very noticeable when the rainbow is very bright.
The brightness of the rainbow depends of the size of the raindrops. Large drops will produce narrow bows with very intense colors. Small drops will produce broader bows with less bright colors. When the drops become even smaller, the colors will fade gradually, and you will end up with a colorless arc, better known as a cloudbow and fogbow.
A rainbow is often companied by a second bow, less bright, and a bit higher in the sky. Perhaps you never noticed that the colors of these second bows are inverted. The start from top to bottom with violet, blue, green, yellow, orange, and red. The funny thing is, the sky between the two bows is noticeable darker than elsewhere. It is called Alexander’s Dark Band. There are occasions when a third bow can appear, although I never witnessed that.
When you look carefully at the primary rainbow, you might see some green, pink, and purple fringes. The amount and spacing of these fringes vary from minute to minute. The fringes are called supernumerary bows. This optical effect will be more visible when the raindrops are very similar in size.
A rainbow can be seen at any place where small water drops form. Not only during rain showers, but also from a water hose at your own garden, or near waterfalls. Officially these rainbows are called spraybows. When you are near a waterfall, make sure you have the sun from behind and there is a big change you will see a spraybow. By following the trajectory of the sun through the sky, it is even possible to predict where a bow might form. This can help finding a great composition for your photo.
While sunlight produces rainbows during the day, moonlight can also produce a rainbow, called moonbows. These moonbows are very rare because the moonlight is not very bright. You need an almost full moon, rain opposite to the moon and you need to be at a very dark location. The biggest change of catching a moonbow is near a large waterfall at full moon.
Although I have captured halos around the moon, and moondogs, I never had the change of captured a moonbow.
Never use a polarization filter when you photograph a rainbow. By polarizing the light, the rainbow will disappear. It is not necessary to completely remove the polarization filter, but you need to turn the filter until the light is not polarized. The effect of polarization is visible in the before-after examples I shot of the waterfall Fossa during my recent trip to the Faroe Islands, and in an older example I shot in the Austrian Alps.
When want to photograph a rainbow, don’t wait until you see one. Make sure you already are at the location where you would like to shoot the rainbow. And if you see one, just photograph it. Don’t care about composition yet, because you never know if it will stay visible for long. After the first photo, you have the time to find a composition. Who knows, perhaps the bow may become brighter.
Although you may feel like shooting the complete bow in one frame, it may be interesting to capture only a part of the rainbow. You can even play with a shallow depth of field, showing the rainbow colors in the background of your subject.
The best time to shoot a rainbow is often during sunrise or sunset, because the bow is at its highest place in the sky. It can be very large and impressive, requiring an ultra-wide-angle to capture it in one frame. If you don’t have a lens available that is wide enough, shoot a panorama while holding your camera vertical, and stitch the individual images in Lightroom (or similar editing software). You might even capture a so called redbow, which is basically a rainbow in a reddish sky that can occur during rain showers and a setting sun.
With the sun low at the horizon you might capture your own shadow also. By choosing your foreground wisely it may become easy to use the clone tool to remove the shadow. But you can also use trees or other objects to hide your own shadow. Or just keep your own shadow in the frame. Just be creative with this and try different things.
Not all colored bows in the sky are rainbows. Halos, arcs, iridescent clouds, coronas, and sundogs are not considered rainbows, although they may show the rainbow colors. The difference is quite easy; rainbows are produced by light reflecting in raindrops, all the other ones are produced by light reflecting in ice crystals. But often these optical light effect are very photogenic also.
Have you made beautiful or special pictures of rainbows, moonbows or fogbows? Please let me know in the comment below, and I invite you to show that image also.