Circular Polarizing Filters are used to increase color saturation, like darkening blue skies so that white clouds stand out. It eliminates reflections from non-metallic surfaces like glass and water. It helps reduce softness in scenery caused by atmospheric haze.  This filter will not change the overall color balance of a photograph. Polarizers are commonly used to control glare on water and to allow the camera to see below the surface. They are also used to reduce glare on car bumpers and to control reflections on plate-glass windows. Polarizers are so versatile that they can perform the opposite functions as well. Some cinematographers use polarizers to increase or enhance reflections, simply by changing the filter?s setting. "Circular" refers not to the shape, but a special design that does not interfere with metering of auto exposure or auto focus systems There is virtually no limit to the new ways Directors of Photography find to use effective polarizers. A few examples of what they can do include: Darkening skies in color photography for dramatic impact. While graduated neutral density filters can also be used to achieve this effect, the need to position their transition line accurately precludes their use in many applications. Polarizers do not suffer from this limitation. Suppressing reflections and capturing truer color when filming actors through a windshield, and from other rigged-car camera positions. Greatly adding to the drama and appeal of the shot...