Friday, September 08, 2006

divergent light rainbows

Fogbows have a similar origin to rainbows. For this reason, Christian Fenn, who had previously photographed fogbows made by divergent light, decided to attempt to image a divergent light rainbow. On 19th April in Hammelburg, Bavaria he managed, in pouring rain, to image a rainbow formed by light from car headlamps.

A divergent light source can actually produce a multiplicity of rainbows, not only of angle 42° but at larger angles also. The net result is that the bows overlap and a discrete coloured arc is no longer visible. Another negative factor is that the rainbow cannot develop a high intensity like those sourced by the sun because only a narrow range of rays fall on the "rainbow cone" having its tip at the observer's eye. To see a divergent light bow it is necessary to be far away from the light source so that its rays are as parallel as possible and develop a bow of sufficient contrast.

In the photograph the divergent light bow is wider horizontally than vertically. This is because the two car headlamps each form bows and so produce an apparent broadening.

2 comments:

Claudia Hinz said...

Here still the link to an article from Christian Fenn about this topic.

Michael Ellestad said...

I made a fine example of a divergent light rainbow when rain in the form of mist droplets and both bows were colorful and well-defined. I need to post them tomorrow.