What does a polarizing filter do?
Light moves through space, vibrating as waves in many different directions. Light which is polarized, however, only vibrates in one plane. A polarizing filter or polarizer is a lens filter which polarizes light along one plane. This can cut non-metallic reflections and enhance contrast under certain conditions. Polarizing filters contain a layer of polarizing material which is laminated between two glass circles and mounted in a frame. You can then rotate this filter, which affects the amount of light passing through. Even at their brightest setting, however, polarizing filters reduce the amount of light entering the lens – they always cost a stop or so of light. So what use are they? Well, polarizers are useful for cutting reflections from water and glass (ie: non-metallic) surfaces. They re commonly used for cutting reflective glare off of windows, or for taking a photo of a lake without a reflection on the lake surface, for instance. They can also be used to darken blue sky (technic
