The polarizing filter
used with most modern cameras is a circular polarizer
. The first stage of the polarizer is a linear filter
which filters out light that is linearly polarized
in a specific direction. The second stage, for technical reasons related to the auto sensors within the camera, then circularly polarizes
the light before it enters the camera.
The polarizing filter has two applications in both color photography
and black-and-white photography
: it reduces reflections from some surfaces, and it can darken the sky.
Light reflected from a non-metallic surface becomes polarized; this effect is maximum at Brewster's angle
, about 56° from the vertical (light reflected from metal is not polarized, due to the electromagnetic nature of light). A polarizer rotated to pass only light polarized in the direction perpendicular to the reflected light will absorb much of it. This absorption allows glare reflected from, for example, a body of water or a road to be much reduced. Reflections from shiny surfaces of vegetation are also reduced. Reflections from a window into a dark interior can be much reduced, allowing it to be seen through. (The same effects are available for vision by using polarizing sunglasses
Some of the light coming from the sky is polarized (bees use this phenomenon for navigation). The electrons in the air molecules cause a scattering of sunlight in all directions. This explains why the sky is not dark during the day. But... Read More