Polarizing filter (photography)

A polarizing filter or polarising filter (see spelling differences) is a filter that is often placed in front of a camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea. Since reflections (and sky-light) tend to be at least partially linearly-polarized, a linear polarizer can be used to change the balance of the light in the photograph. The rotational orientation of the filter is adjusted for the preferred artistic effect.

For modern cameras, a circular polarizer (CPL) is typically used, which has a linear polarizer that performs the artistic function just described, followed by a quarter-wave plate, which further transforms the linearly polarized light into circularly-polarized light. The circular polarization avoids problems with autofocus and the light-metering sensors in some cameras, which otherwise may not function reliably with only a linear polarizer.