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Photographing Rainbows

Rainbow photo by  Eric Rolph,     You can see the clear inner one and just about see the outer one, click the  images to see larger version.

Before we look into the detail on how to photograph rainbows, lets look over a few facts about them.

Rainbows are caused by light being bent through particles of water. Nearly always seen best when the sun is behind you and the rainbow in front of you. 

There are often two rainbows an inner one and fainter thicker outer one, although this is not always easy to see, the brighter inner rainbow has blue on the inside and red on the outside and the lighter outer one, if visible, is the reverse of this. The area between the two rainbows is darker than the rest of the sky, and the area inside the bright rainbow may be noticeably lighter. The diagram on the right shows the sequence of the colours of the inner brighter rainbow.

You can also get rainbow effects from mist, waterfalls, fountains, spray bows from sea spray, moon bows by moonlight. You can create your own with a garden hose and holding it away from you with your thumb over the end and with the sun behind you. Rainbows may also come of glass vases, CD and DVD disks and from water where you have a mirror or mirror like surface at an angle in the water.

A rainbow does not actually exist at a particular location in the sky. It is an optical illusion whose apparent position depends on the observer's location and the position of the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer's eye. This light is what constitutes the rainbow for that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior. The bow is centred on the shadow of the observer's head, or more exactly at the antisolar point (which is below the horizon during the daytime), appearing at an angle of 40°–42° to the line between the observer's head and its shadow. As a result, if the Sun is higher than 42°, then the rainbow is below the horizon and cannot be seen as there are not usually sufficient raindrops between the horizon (that is, eye height) and the ground, to contribute. Exceptions occur when the observer is high above the ground.

There are other variations caused by reflections and a variety of other factors that can produce some rare results like several rainbows coming from a common point.

To photograph an entire bow requires a camera angle of 84 degrees, a 12mm lens on a digital camera  like the D80 or D300 has a camera angle of 90 degrees. With FX or a 35mm camera you would need a lens of 19mm or wider. From an aircraft there are occasions where a full 360 degree circular rainbow can be observed.

There is another optical illusion that is far smaller, but can be mistaken for a rainbow, and this is only 5 to 20 degrees wide, and is known as a glory or anthelion. This can be small and circular around a person or object, or projected from this object,  but always away from the sun. They often appear like circular rainbows but can be fogbows that resemble eliminated halos. This is most often seen when in aircraft around the aircrafts shadow. The photographic challenges with these are similar to rainbows.

Rainbow photo from Wikipedia Rainbows can often be seen coming from the mist of Waterfalls .   Click image to see a larger version

So rainbows and glories are optical illusions, but quite well understood, with a lot of material written on them over many centuries. By definition you are unable to stand at the end of a rainbow that you can see but could stand at the end of a rainbow that another cold see.  The rainbow arch we see is unique to us, and when moving will often appear to move with us.

Rainbows can be made with a hose. This image shows the water, but used as a fine spray rainbows without the hose jet is possible. I think this image is from  a garden/lawn sprinkler. I have created much larger ones with a hose in the garden by putting my thumb over the end so as to shoot it high into the air as a fine spray. I must have a go at photographing one of these.

So how do we photograph a rainbow if its an illusion

Rainbows can be photographed exactly as seen, you cannot spot meter off them, nor can you focus on them.

Exposure   - In the days before we had exposure metres in our cameras or loose, we had EV Tables,  with these you could look up many situations, be it a flood lit circus, a moonlit night at a set phase of the moon or a rainbow, and we have produced a set of EV tables, that are a later developed version from the earlier form, allowing for the higher ISO values in use today.

In these tables it shows a normal sun light day at 100 ISO to be an EV value of 15, where a rainbow against a clear sky is achieved with an EV of 15 and against a cloudy sky with an EV value of 14. A typical scenic in hazy sunlight is also shown as an EV of 14. From this we can see that there is no real difference at all in exposure required to photograph rainbows, and that a correct exposure that records the scene and sky will record the rainbow.

In practice when using RAW format, as opposed to JPG, you can underexpose slightly, by say half a stop, so you can make a greater correction than this after if you want, and by this means you can probably record greater colour saturation. Then you use adjustments in your RAW converter, be it Photoshop or Capture NX2 or some other, you will lighten the greys more while retaining the colour.

Colour - White Balance We have no way to set the white balance specific in any way to the rainbow, and as it has all colours we can't enhance it by moving the colour one way or another. Some people do like to warm things a little, making the red end show up more. Generally you can set the white balance for the lighting conditions as you see them, although auto white balance also will usually produce satisfactory results. As long as you are shooting in RAW you can of course change the white balance to any other preset after if you wish. Rainbow brilliance varies The brightness or brilliance of a rainbow will vary, it can be weak, right through to very strong, and will change generally over time, often fading before it completely disappears. You want, if you can therefore, to take a number of photos and select the most effective one.     Image right - end of the rainbow, yes you can use a telephoto lens to get a closer view.   Photo by  Wing-Chi Poon

Viewpoint

The best viewpoint is higher up, so while in theory you would see many rainbows most times you see them when you have a good view. If you want to look for rainbows try showery days and sit high up on a viewpoint looking directly away from the sun.

Concluding

Over the years I have photographed many rainbows, some coming out far better than others, often having missed the best of them by the time I got the camera out. Most of my examples were shot back when I was using film, and at one point lived in Wales. At that time I was living high on the side of a valley where the sun was behind the house and my home/office was at the front, and I saw at that time very many rainbows.

Not a rainbow. Glory photographed by Mila Zinkova
Glory taken by looking down from a high bridge into or through mist By Mila Zinkova