Polarizer filters are among the most
versatile filters that are used. Below are some of the basic functions
of polarizer filters:
Polarizer can remove most reflections
from nonmetallic surfaces such as glass, some foliage, water, plastic,
and fabric colors.
Polarizer filters are the only filters
that darken a blue sky and increase contrast between sky and clouds.
As polarizer filter can remove blocking
reflections, it can also increase the overall color saturation.
Polarizer filter can reduce overall scene
Polarizer filter function much like a
neutral density filter.
Polarizer filters are made of a myriad of
extremely small (microscopic or smaller) crystals oriented like a
Venetian blind. The crystals block light waves vibrates at angles other
than parallel to the crystals. Light waves vibrating parallel to the
crystal array pass between them. Much as the light passing through the
slats in a Venetian blind is controlled by changing the orientation of
the blind slots, so turning the rotating polarizer in its mount acts to
block the polarized light attempting to pass through.
The effect of the polarizer filters on a blue sky is to darken it at
certain angles. The most efficient angle is a 33 arc made by the
filter and the reflecting surface. As the polarizer filters block much
of the light attempting to pass through it, exposure must be increased
to compensate for the light loss. Generally, polarizer filters will
impose around 1.5 f-stop light losses but this will depends on
Other than darkening blue skies and increasing sky/cloud contrast,
polarizer filter can also increase color saturation of many objects by
reducing diffuse reflections on the subject's surface. Employing a
polarizer does not change or add color; its use allows color to be
recorded as a richer, deeper, and unmasked hue, all but free from
color-robbing reflections. It may seem strange, in view of the
increases in color intensity of polarized subjects, but these filters
can actually reduce overall scene contrast, particularly in scenes
containing major areas of blue sky. By darkening a blue sky, a
polarizer diminishes its brightness. The highlights represented by the
sky and any shadows in the scene are brought closer together with a net
result of a lower contrast range.
An added benefit of this contrast-controlling technique is that shadow
detail can be given more exposure without overly lightening the sky. In
essence, polarizer filters act much like a moderate neutral density
filter and reduce contrast by about one full f-stop. Polarizer filters
can also remove reflections from glass and water surfaces. The amount
of surface reflection that is eliminated depends upon the angle of the
polarizer to the subject. There are still further uses for these
ubiquitous filters. They cut through light and moderate haze by
blocking the haze, allowing polarized light to pass through the lens.
There is no one best way to employ a polarizer. The only clear
recommendation is not to overuse it. Even though polarized color is
often intense, it cannot save an otherwise weak picture. The best way
to judge the effect of polarization is by direct observation. To
achieve maximum effect, move the camera 90 to the sun. You should be
able to observe the filter effect right in the viewfinder as you rotate
the filter in its mount.
In black-and-white photography, the filter is used as you would a red
contrast filter. Expect significant increases in contrast between the
darkened sky and lighter objects in the scene. Polarizer filters are
brought into use to control overall black-and-white scene contrast on
bright, sunny days by absorbing and reducing secular highlights, thus
bringing all light values in a scene closer to one another.
To find the part of the sky that will be most affected by polarization,
point your forefinger at the light source with your forefinger and
thumb circumscribing a 90 arc. As you rotate your thumb, it will
describe an arc indicating the polarized portion of the sky.