Polarizing Filters

These deservedly popular filters, also known as polarizers, use the inherent polarization of atmospheric scatter, glare and other unwanted reflections to remove such photographic pests selectively and prospectively from the light entering your camera. If you shoot much outdoors, the ability to mount a polarizer is reason enough to invest in a filter-capable camera and the required adapters. No single filter type will deliver more benefit in routine photography than a properly used polarizer.

Linear vs. Circular
Polarizers come in two main types, linear and circular, identical in use and effects and differing only in camera compatibility. Specifically, linear polarizers are incompatible with cameras that rely on split-beam optics for functions like metering and auto-focus. High-end digital SLRs may require circular polarizers, but the less expensive linear polarizers will work with most digital cameras, SLRs and rangefinders alike. When in doubt, get a circular.

Benefits and Use
Used properly, polarizers can darken the blue of the sky, highlight clouds, suppress unwanted highlights and improve general color saturation by suppressing atmospheric scatter and color-robbing reflections off water, glass, sunlit foliage, vehicles and even bald heads. (In wide-angle shots showing lots of sky, however, you may get better results with a GND.)

Polarizers are admittedly more complicated to use effectively than one might hope, but once you develop an understanding of the ways in which scattering and reflection add polarization to light in the photographic environment, polarizers become very simple. Digital rangefinder users often complain that they can't see their rear LCDs well enough in bright sunlight to adjust a polarizer properly under TTL (through-the-lens) control. But as long as you're after maximum effect, you can easily learn to adjust a polarizer reliably without TTL control.

Polarizers always require substantial exposure compensation. In strongly polarized ambient light, a polarizer can easily cut to 3-4 stops or more. In the absence of polarized light or when set at 90° to the prevailing target polarization or target directions—most polarizers end up acting as 1- to 2-stop (0.3-0.6) neutral density filters.

Digital cameras with limited dynamic range can benefit greatly from the selective suppression of excess contrast. It's often best to reduce exposure to preserve highlight detail and work to bring up the shadows in post-processing—for example, using tone curves or gamma adjustments. You may well end up with noise in the shadows, but that's usually preferable to blown-out highlights. The more you suppress the highlights with a polarizer beforehand, the fewer problems you'll have in the shadows.

Due to the limited UV sensitivity found in most digital cameras, polarizers also provide a welcome and effective alternative for haze control at favorable camera-sun angles.