Kauai Fogbow and Rainbow

December 27, 2010


Photography: Neil Libby
Summary Author: Neil Libby; Jim Foster

The photo pair above showing a bleached fogbow (top) and a much more colorful rainbow (bottom) was taken from Kauai, Hawaii on November 29, 2010. The setting for both photos is the Kalalau Valley, but the fogbow was snapped at Pu'u o Kila Lookout and the rainbow was snapped about 1 mi (1.6 km) to the west, at Kalalau Lookout. Intermittent showers greeted us on our little excursion to the 4,000 ft (1,219 m) valley overlooks, but on occasion breaks in the clouds permitted the Sun to shine appear.

Rainbows owe their coloration to refraction and reflection in raindrops. In general, the larger the drops are, the more eye-catching the colors will be. Fog and mist droplets; however, are considerably smaller than raindrops and wave interference (diffraction) becomes more important than refraction in sending light toward our eyes. In essence, when the droplets are smaller, wave interference increases, the wavelengths of light overlap and so colors are washed out.

Photo Details: TOP - Camera: COOLPIX S220; Focal Length: 6.3mm (35mm equivalent: 35mm); Aperture: f/4.6; Exposure Time: 0.0015 s (1/686); ISO equiv: 80. BOTTOM - Same except: Exposure Time: 0.0013 s (1/797).