Interference and Drop Curvature

A good example of white light fringes caused by reflection off the changing curve of the droplet, near the attachment to the grass. The positioning is very critical as shown by the examples below, from a different drop.

Strong white light reflection fringes Guttation drop hanging from a grass blade

The camera angle was changed by just a few degrees between exposures to reveal the behaviour around the neck of the drop in the images below. The images on the right show the matching reflection point on the drop. The sun was about 58 degrees up and the camera was pointing about 20 to 30 degrees below the horizon in the general direction of the sun.

Coloured fringes from a droplet reflection Source of coloured fringes
Coloured and white fringes reflected from a drop Source of coloured and white fringes
White reflection fringes Source of white reflection fringes

The top image shows colour dispersion from the top of the 'saddle' while the middle image shows fringes from both sides of the saddle. The lower image shows white light fringes which must be due to reflection only. It is quite hard to see any difference between the positions on the drop which differ by around 0.1 millimetre or less. The whole drop was little more than a millimetre in diameter.

Canon EOS 20D   27th July 2008
Wiltshire, England

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