Iridescence Through a Window Curtain
March 06, 2014
Photographer: Bertrand Kulik; Bertrand’s Flickr site
Summary Authors: Bertrand Kulik; Jim Foster
The photo above showing iridescence of an aluminum flashing was taken through a curtained window in my home in Paris, France. Looking at the rooftop without the curtain it wasn't possible to see this coloration. Minute cloud droplets may result in cloud iridescence and coronas; however, in this case it’s not droplets that formed the irisation or iridescence but the very fine mesh of the drapery fabric. Light waves coming through the curtain are diffracted as they pass through the tiny (about 0.02 mm in diameter) similar-sized slits. If the mesh sizes are irregular (if droplet size varies substantially in a cloud) or are simply too large compared to the wavelengths of visible light (380-750 nm) the colors won’t be as readily apparent. Note that for irisation phenomena the angle of diffraction is important: The Sun must be relatively near the object being viewed not behind the viewer as with rainbows and glories.
Photo details: Canon EOD 7D camera; 100-400 Canon lens; 250 mm focal length; f/8; 100 ISO; 0.004 sec. exposure.