Fogbow Polarisation

The fogbow is strongly polarised so a filter can have a significant effect on its visibility. This pair of images shows how a fogbow can be enhanced or cancelled out depending on the filter orientation. With the polarising axis along the fogbow (vertical in this case) more of the fogbow light passes through than from the background. Rotating the polariser 90 degrees cancels out the bow so it is lost in the background.

However things aren't really that simple. Switch quickly between the images and look carefully at the dark gap inside the main bow. With the polariser horizontal there is in fact a faint coloured band roughly where the dark gap lies on the vertical polarisation. This weaker band seems to follow the glory polarisation direction. The glory is clearly visible round my shadow at left and changes shape with the polarisation.

Click here to change angle of polariser

Fogbow and polarisation

In this particular case there is something else which adds to the complexity.

There seems to be a subtle change of droplet size near the top of the fog, which shows up as a change in curvature of the fogbow.

The orientation of the polariser is shown at the bottom left of each image.

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Canon EOS 20D   11th December 2005
Wiltshire, England

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