A rainbow alone rarely makes an interesting image, unless it's extraordinarily vivid so that it becomes the main subject in an otherwise drab scene.
Some of the best rainbow photographs include other dominant objects, with the rainbow used as an accent or visual prop in the composition.
Let's look at some examples.
(Left) Bob Peavy has aligned the sweeping curve of the road with the tip of the rainbow, and set the graceful arc to embrace the large tree.
These foreground elements make the rainbow photo exciting and adventurous, topped off by the double rainbow visible against the dark cloud.
Luck plays a part anytime you're seeing such rainbows, but you still have to use your skill to compose an interesting photo.
That can be all the more difficult if rain is pelting down, so practice and forethought are helpful.
At the end of the rainbow you'll find one of two things, and neither is a pot of gold:
either (1) dry air (the rainbow ends with the last water droplets) or (2) shadow (of a cloud, building or mountain) where the sunlight no longer illuminates the droplets.
Given a large sheet of rain in full sunlight, rainbows would appear as complete rings if the earth didn't get in the way.
In fact, they can appear as full rings when seen from the air.
photo by Kent Mason
The point where your rainbow intersects the earth has potential for a great image.
If you have the mobility (such as a vehicle and open territory), or if you plan ahead using our Rainbow Planner,
you may be able to position the end of the rainbow exactly where you want it.
Technically, as you move you're viewing many different rainbows, but the point here is that you can exercise some degree of control over its apparent position.
Try composing with different subjects featured at the end of the rainbow.
For example: locate an object of interest near the end of the rainbow, with the colored bands of the rainbow's arc intersecting the object or offsetting it within the frame.
If you have a long telephoto lens, try framing a distant subject with the rainbow's arc.
The longer your focal length, the more you'll magnify the rainbow into broad color bands, while reducing the apparent curvature.
In the photo above right, Kent Mason has created a strong composition using the sweeping arc of a strong foreground shadow as a leading line toward the base of the rainbow.
A short telephoto or normal lens can effectively combine the foreground with the distant rainbow and horizon in a unified image.
Notice here how the rainbow is nearly vertical as it intersects the horizon.
After reading about Rainbow Angles later in this article, you'll recognize this as a sign that the sun is very low in the sky.
Late in the day, rainbow arcs are the most broad, and hit the ground at steep angles.
Photo by Bob Peavy
Try a wide angle lens to include more of the arc, so the rainbow becomes more semi-circular in appearance.
The widest arc you can see from the ground is a half-circle at sunset or sunrise (see Sunset Rainbows).
If you're lucky enough to encounter both ends of a rainbow with the sun sinking low,
you can capture it with a 135-format camera and a 20-mm lens (having 84° horizontal field of view).
See Bob Peavy's 24-mm wide-angle shot (left) for an example of a late-afternoon rainbow arc.
With the sun higher in the sky, you can capture a full arc with a 28mm or longer lens.
The choice of angle-of-view will probably be driven more by your subject than how by much of the rainbow to include,
but try different things for as long as the rainbow persists (usually not long at all).
A zoom lens will let you experiment with compositions much faster!
Double Rainbow by Tom Field
Capturing the entire arc of a big rainbow indicates a sweeping landscape shot, typically using a very wide-angle lens.
This doesn't mean that your subject must be the landscape alone.
Often the sun may offer you a scenic, broad rainbow while spotlighting some foreground object such as a tree or flowered hillside.
The trick here is not only balancing the foreground luminance with the dim background, but exposing such that any wind-induced motion in the foreground doesn't smear the object.
It's best to pick foreground objects that are not affected by the wind.
More rare is the dark cloud that casts a heavy shadow on your foreground, with possibilities for an extraordinary silhouette of your subject against a rainbow panorama.
Again, a non-moving foreground silhouette is far easier to work with.
This type of shot is probably best with a wide-angle lens, to maximize depth of field and include a significant arc of rainbow.
When the opportunity arises, compose on the run and shoot quickly with whatever you have before the moment is gone.