One way that polarizing filters are used is with water, as well as other reflective surfaces. Polarizing filters significantly reduce glare, making water and reflective surfaces appear more transparent. This effect is limited by viewing angle, however, and a head-on view will give a more transparent result. These filters can also intensify the color of water, though this effect will depend on the strength of the filter used.
Polarizing filters also have a significant effect on the sky in a given photo or film clip. Rotating the filter to adjust the strength of the polarizing effect will shift the sky from a natural pale blue color, to a vibrant and deeper blue. This technique can yield different effects under different weather conditions or at various times of the day and is often used to enhance the look of smoggy air in urban photography.
Another way that polarizing filters are used is to control the color of a shot. Many objects appear brighter under a polarizing filter since these filters block small reflections that may be unnoticeable. This is especially true in outdoor conditions, where many surfaces are glossy and reflective, for example, leaves in tress and blades of grass.
Polarizing filters are split into two basic types: circular and linear. Linear polarizing filters are less expensive than circular ones, but they render through-the-lens metering and autofocus unusable. All cameras made after 1970 with an autofocus feature, with the exception of view cameras, require and use a circular polarizer.