Nick Jenkins is a photographer who is associated with both the Royal Photographic Society and the Welsh Photographic Federation. He specialises in taking pictures of British landscapes and he also works on holidays for Light & Land Photographic Holidays. You can visit Free Spirit Images for more information.
Here's his tip:
"Photographers often extol the virtues of polarising filters to get those blue skies bluer and the white clouds whiter. Because of the polariser's ability to reduce or remove reflected light this is absolutely true, provided, of course, that the camera is more or less pointing at 90 degrees from the sun, i.e. the sun is to your left or your right.
However, this ability of the filter to reduce reflected light can also come very much into its own when photographing water. It is only when you apply the polariser and turn the outer ring that you can clearly see just how much the surface of the water does reflect light.
These two images were shot last week at Clappersgate in the Lake District. The river is the Brathay, coming down from the Great Langdale valley. I find that the shot using the polariser at full rotation really boosts the autumn tints (greens and browns) and by holding back the reflected light off the surface of the river, gives me a much more pleasing rendition and places greater emphasis where I want it - on the rock and riverbank.
Don't just use polarisers on bright, sunny days for landscapes. They have a whole array of uses!"
(for info. shot on a Nikon D300 using a Sigma 24-70 f2.8 lens and a Hoya circular polarising filter, on a Gitzo tripod. Aperture f18 at 2.8 seconds for both shots at 200 ISO).