Rainbows are among the most beautiful natural phenomena, perfect for enhancing a dramatic-lighting vista or becoming your main subject in an otherwise uninteresting scene.
This six-part article discusses where and when they may be found, how they form, and recommendations for photographing rainbows.
Rainbows can be quite commonplace when conditions are right.
Or they can delight with their surprise appearance in unusual places.
But the colorful arcs always thrill the observer and, when used effectively, can add a "wow" to photographs.
Rainbows appear under specific and well-defined conditions.
Although you can't always predict when these conditions will occur, at least you can recognize when a rainbow is likely to form and prepare to make some great photographs.
Better yet, you can be a rainbow chaser: put yourself in the right place at the right time and know exactly where a rainbow is likely to form.
Anticipation and preparation are essential for the photographer, because rainbows can be fleeting:
appearing and disappearing, shifting in and out of your composition, and fading from brilliant to faint in seconds.
Be ready to take advantage of an eminent rainbow, and you'll maximize your chances of creating a great image.
Hyde Park Fountain, London
There are two common conditions under which a rainbow is visible, but they are caused by the same phenomenon (see How A Rainbow Forms).
First, sunlight hits raindrops in the sharp edge of a rain storm.
The raindrops can be falling, or they can be swirling within wet clouds.
Second, sunlight hits the spray from a robust waterfall, geyser, or fountain.
In both cases, the water droplets must be at least a certain size for the rainbow to show.
The microscopic drops in mist or clouds do not produce a rainbow (which is why we don't see Technicolor clouds!) nor does frozen water, such as snow or hail.
However, droplets of morning dew on grasses or spider webs can be made to form a rainbow if you are in the right position.
photo by Kent Mason
So when does a rain storm have a sharp edge bathed in sunlight?
Typically this occurs as the trailing edge of the storm moves past your location and the sun reappears.
As a bonus, the dark storm clouds make a dramatic and contrasting backdrop for a vivid rainbow.
The good news here is that the rain has likely stopped so you shouldn't get wetter.
The bad news: in order to get to a good vantage point and scout your compositional possibilities, you were probably out in the rain anyway.
Timing is critical, for passing showers can recede quickly or the sun can go behind another cloud bank.
Your perfect rainbow may refuse to wait around while you relocate to get a better composition.
That's why predicting the location of a rainbow using our Rainbow Planner can improve your chances.
Spray can be much easier to deal with than rain: all you need is sunlight at the right angle and plenty of continuous spray.
Begin with morning or afternoon sun, because rainbows won't be visible from ground level until the sun falls below 42 degrees above the horizon (see How A Rainbow Forms).
Continuous spray from a fountain or waterfall may give you more time to work the scene and find pleasing compositions,
but beware of shifting wind which can move the spray in and out of your rainbow.
And the sun advances rapidly, so the rainbow may still last only a few minutes unless you relocate.
Bright sunny days make bright rainbows, but they may not show up so intensely on film if the background is also brightly lit.
Try for a darker background if possible.
A geyser may be less cooperative than a waterfall or fountain, forcing you to wait for an eruption and then work quickly.
But using modern eruption-time predictions and accurate weather forecasts you can at least try to be present when the possibility for a rainbow is greatest.
(To left: Castle Geyser forms a rainbow in late afternoon, Yellowstone National Park)