Rainbow Photography

 

Finding the Pot of Gold

Rainbows have always been a popular subject for photography. They are among the most dramatic and colorful of the natural phenomena. It is little wonder that rainbows have always been a subject of superstition and mythology, and our scientific understanding of their origins and behavior has only minimally diminished our sense of wonder at their surprising beauty. Part of the mythology about rainbows describes a Leprechaun's elusive pot of gold that can be found at the end of these colorful celestial arcs. Of course a rainbow is not a physical structure and it's end can never be defined, but I would suggest that, in a photographic image, a rainbow can have a visual pot of gold and that treasure has to do with the strength and interest of the foreground.

Not Just a "Pretty Thing"
Photographs of rainbows always show a lovely spectrum of colors, but the best images are more than just a "picture of a rainbow".  It is the surrounding compositional elements which provide a sense of place and context, that makes a rainbow image compelling and not just a snapshot of a colorful "pretty thing". This is actually one of my central compositional rules. A great landscape photograph is seldom just a picture of a" pretty thing". Whether it is a spectacular mountain, a quiet lake or a colorful autumn tree, images are made especially memorable by how you arrange the elements around the "pretty thing" to provide contrast, context, balance and to draw your eye. This particularly true of rainbows.

Foreground Hunting

Chesterfield New Hampshire Town Hall

When I see a rainbow forming my first thought is "Where can I go
to place something interesting in front of the color".  An immediate corollary of that thought is, "How far can I go before the rainbow disappears and from what angle is the light coming".  I was working in my studio one afternoon when I noticed a beautiful rainbow forming in the eastern sky. I grabbed my camera and leaped into my car.  I knew that time was fleeting, so I headed up to Chesterfield Town Center and arrived just in time to have about 2-3 minutes of the bright colors, against the dark sky, before the sun sank into the clouds. The colors were beautiful, but It was the old stone town hall, bathed in the sunset glow that made this picture special. 





The Physics, I Promise, NO Equations
Sometimes catching a rainbow in a great location is a matter of

Light Through a Raindrop (Wikipedia)

luck, but a basic understanding of the physics of rainbow formation can help you improve your chances. Rainbows are formed by the summation of light refracted and reflected through millions of rain drops. The light is refracted (bent) as it enters the drop. Light of different waves lengths or color are bent by different amounts during refraction, the red light is bent less than the blue, creating the rainbow effect. The light is then reflected off the back of the drop and refracted once again as it passes out of the drop and on to your eye. In the atmosphere, the reflected light comes out of the drop at an angle of about 42 degrees down from the angle of the sun's rays. The light can actually bounce around in the raindrop twice creating a secondary rainbow which is less intense and  is seen above the original.  Interestingly secondary rainbows show the colors in reverse order. Tertiary rainbows are also possible, but are quite rarely seen.

Double Rainbow

My goal here is not a physics lesson, but the physics does provide some helpful photographic lessons.

1. First rainbows are always most intense when shot with your back to the sun. A simple way to think of this is to try to place your shadow on a line between the sun and your foreground subject.
2. The colors become more intense as the sun drops toward the horizon and, because of the angle of refection, rainbows don't generally appear until the sun drops to below 42 degrees in the sky. Before that time, unless you are at altitude, the rainbow is actually below the horizon. In southern New Hampshire, during July, this means that we would not expect to see rainbows until after 4:30 in the evening.
3. Of course you can't have a rainbow without the combination of raindrops and sunlight. Most often this comes from a clearing storm, but fog or sea mist may also create a rainbow. The best bet is to wait until the first light after an evening storm has past by and look away from the sun. With luck, the rainbow will be shining against the receding dark clouds.
4. Finally, since rainbows are often fleeting and pop up unexpectedly, you might want to keep your own list of prime observing sites close to home. Look for interesting foregrounds that can be viewed against the eastern sky with the sun at your back.  Technology can help improve your odds of finding a great show.  Using my IPad I can now follow the progress of storms on radar and then find the best locations using the Photographers Ephemeris to discover the direction of the sun at any time.

So keep your eyes on the sky after a storm, feel the warmth of the sun on your back, watch the foreground and you may just find your own pot of gold.