| Altocumulus with iridescence around 2.30 PM on 23 May 2003. The display lasted about 15 minutes with two peak periods as the sun and cloud 'just' overlapped or 'drifted in and out'. The colors shown here are fairly accurate and true to the original transparencies and as close as I could possibly match them. I've only added a touch more contrast to help them resemble the electric intensity (like very bright neon light or the reflected light off a CD). Softer pastel shades of color were also visible as well as areas of very intense color. Exposures were made on Fuji Velvia at around 2000th sec at f16. Looking through the viewfinder with a 300 mm lens attached I was in awe at the colors I was seeing. Violet / Blue patches (not recorded on the film) in the dark gaps between the cloud were particularly vivid too but 3 or 4 'stops' less bright. I was thinking at the time it's just a pitty that these colors don't (usually) record on film the way you see it in real life. But this time when I had the film processed I was amazed at how well it reproduced although obviously a bit paler and less bright than to the eye in real life. I explained to Rob (my Color Lab technician) that I'd used no filters. If I hadn't known him for 20 years I don't think he would've believed me. I've photographed iridescent cloud a few times before but never have I seen or recorded anything as good as this event. Spectacular cloud structure seemed to make it more photogenic this time. Camera position relative to the cloud and sun seemed to be fortuitously ideal too. The sheer brightness (being only a few degrees off the sun) means that few people actually notice it, however it was strikingly visible by just holding up your hand to mask the suns disc.
Elements that did not record on film. In areas of dark or seemingly clear sky there was a bright but very deep electric blue/violet color. It was visible in all the small gaps in the cloud but just within the coronal area (about 5 to 10 degrees around the sun). This was apparently background Cirrus or Cirrostratus being illuminated but seemingly in only the one uniform color. Being 3 to 4 stops dimmer (but still very bright) it did not record in these exposures and yet it was very evident when I was looking through the 300mm lens while taking the photos. Combined with the very bright areas of Altocumulus it was absolutely amazing and much better than these photos can portray. Through the telephoto lens I could also see it very slowly rippling and changing as the cloud and sun moved position. Warning : Don't try this at home if you ever see it. But if you must, use a steady tripod to help prevent accidently aiming the lens directly at the sun. Also, don't use a digital camera or it will surely damage the CCD sensors.
The bottom three photos were taken with a 35mm wide angle lens to show the surrounding sky and cloud. The last two images have been cropped. (Note: 'Cr' after a file number indicates it's been cropped.)
Iridescence in cloud is fairly common and occurs to lesser degrees on many days of the year but displays like this one are perhaps once in a lifetime.
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