Polarizing Filter - Do You Need It?
A polarizing filter is a neutral grey glass filter with two independant rotating layers. Known as Circular Polarizers (or CP), the back layer screws on to the lens, while the front layer is free-rotating. Rotating the front layer varies the amount of polarization, which reduces reflections by varying degrees.
Reflections: Polarizers are also employed to "see through" reflective window displays, giving the image a clearer view, improved contrast, and deeper saturation.
Sky: Polarizers are most famously used for darkening the sky, giving the clouds better definition against a bluer sky. Maximum effect can be achieved when the sunlight is at a 90 degree angle to the camera. If the sunlight is directly in front of or behind the camera, then the polarizer has no effect.
Studio: In the studio, polarizers are employed to reduce reflections on products and food, thus preventing hot spots from studio strobes.
Landscapes and seascapes: Polarizers cancel our reflection from foliage and water, preventing the inadvertant underexposure caused by the bright reflections.
Polarizer is ineffective against metallic surfaces.