Polarizers provide colour and contrast enhancement. Reflected light often shows up as whitish glare that washes out colour in an image.
A Polarizer corrects this problem producing deep, dramatically blue skies. It also removes glare from non-metallic surfaces, such as windows and water.
Colour saturation in general, especially outdoors, can be improved significantly.
A Circular Polarizer has the same effect as a Polarizer and is used on cameras with beam splitting metering systems commonly found on auto focus SLR's (for most 35mm auto-focus cameras see your camera manual).
Area of sky most effectively polarized with a Circular Polarizer: Point your index finger at the sun. With your thumb extended at a right angle.
Essential general-use outdoor colour filter
Produces deeper skies and minimizes reflections in black and white and colour photography
Combine a Polarizer with a Red 25 for incredibly dramatic black and white landscapes
Can be rotated to achieve desired effect
Use the Tiffen Polarizer with the enhancing filter for more dramatic effects