One of the most important pieces of equipment a landscape photographer has is a circular polarizer filter. It can dramatically improve your images. The main reason why you want to use a circular polarizer is that it will increase the color saturation and contrast in your images. The sky will be deeper blue, reds will be deeper red and in short all colors will be more vibrant and "pop" out.

Polarizer	No Polarizer

The intensity of the effect can be varied by rotating the filter. Look towards the sun and rotate the filter and you will notice that the sky turns from light to darker shades. In addition to increasing saturation and contrast, it will reduce reflections off non-metallic surfaces.

Article by Jeremy Baker