A polarizing filter is probably the most useful filter you can use with your camera. It removes polarized light from the image, thus reducing reflections and glare, while at the same time increasing color saturation—especially that of a blue sky. A circular polarizing filter works by rotating an outer ring to vary the amount of polarization that is being filtered. This effect is difficult to mimic on the computer.
Photo by Clifton Beard; ISO 100, f/8.0, 10-second exposure.
Visible light from the sun travels in a straight line as a wave that is oscillating in all directions, such as up and down and from side to side. When that light is reflected off an object, it is the reflected wavelength of the light that determines the color of the object. The rest of the colors are absorbed by the object.
For example, a pure blue-colored object reflects only blue light and absorbs the red, orange, yellow, green, indigo, and violet parts of the light. Likewise, green leaves on trees only reflect green and some yellow, while absorbing the other colors.
If the light being reflected or scattered travels in only one direction—the polarized one—it will cause glaring and reduce the color intensity of the reflected surface. So, by using a special filter to remove this polarized light, the color intensity will be restored.
A polarizing filter has a layer of Polaroid (synthetic plastic) sandwiched between two glass plates. In a circular polarizing filter, as the front plate is rotated, the angle of polarization and thus the amount of polarized light that passes through the filter changes. This allows precise control of the degree of polarized light that is to be removed.
Photo by Matt Hintsa; ISO 200, f/4.0, 1/250-second exposure.
Now, when sunlight encounters atoms in the Earth’s atmosphere, which are mostly of nitrogen and oxygen, the light scatters. Blue light is scattered more than red light, which is why a clear sky during the day appears blue in color.
The electric field of scattered light tends to oscillate in one direction. So, if the photographer is looking perpendicularly to the direction from which the light is traveling, it will be polarized because the energy goes one way.
By applying a polarizing filter, the energy of the light along one axis can only pass through, hence why the filtering effect works best when the sun is at right angles to the direction the photo is being taken, and the sky will appear to be darker blue in color.
If the sun is in front or behind the photographer, the polarizing filter will make no difference because the axis of oscillation will not be filtered by the Polaroid, and thus no effect will be seen.
There are two kinds of polarizing filter available to photographers—linear and circular—but only the circular type will work properly with digital cameras. This is because the linear type affects metering accuracy, as autofocus cameras already polarize some light inside the camera and a false meter reading will be obtained.
Photo by Mat Distef.
Circular polarizing filters are made with a wave-retardation plate exactly a quarter of a wavelength in thickness, which lets the light to passing into the metering system appear unpolarized. However, if you do have a linear polarizer, simply take a meter reading before attaching the filter, and then increase exposure time by a couple of stops. That should do the trick. With film cameras it makes no difference which type of filter you use.
About the Author:
Chris Smith (photography-expert dot com) gives photography tips in his ezine.
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Yes, the physics is all messed up. Visible light is unpolarized when emitted from a primary source. This means that the electromagnetic oscillations may be in random orientations. Reflection at certain angles produces polarisation, that is, it makes reflected light cause oscillations along a specific direction. Hence incident light is unpolarised and reflected light is polarised.
Nice try guys but you messed up a lot of the physics. All light is typically somewhat polarized but that polarization tends to be random. When light gets reflected the polarization of the reflected light is rotated from incident and typically only one polarization comes off the reflected surface. Polarizers work by eliminating that reflected light or the light with a specific polarization. When you rotate the fiter the filter is set to pass or block the wave. That is why you can see into water better when wearing polarized sunglasses as the sunglasses block the reflection. Those sunglasses if worn while viewing throug your polarizing filter can result in all light going away as you rotate the filter. I believe the reason that linear polarizes are an issue on digital cameras is that light is reflected to the meter sensor with a set of very small slots in the DSLR mirror which also polarize the light going to the sensor. A linear polarizer might result in much less light hitting the sensor. Polarizes work on the sky by reducing the amount of reflected light to have the light be cross-polarized needs the sun to be at an angle. .
nice article. About filters–I tried Tiffen, but they did not hold up at all. Two of them broke withing a couple of months. More expensive, but B&W worked the best.
Oh, the windows on airplanes must be polarized in random way. Take the polarizer off.
I once read in Amateur Photographer that combining a Red Filter with a Polarizing Filter
gives results like Infra Red Photography, and tried it with Kodak Portra Film.
The result was fantastic ! I wonder whether the result would be the same with Digital… !
Excellent timing! I bought one of these for an upcoming cruise and now I understand better how to use it!
Absolute love the photographs used in your articles, but would find it so helpful, if you would also include the efix data.
Do polarizers really minimise haze? One landscape I am working on (a valley with the sea in the background) is shrouded with mist (not thick, but annoying) just during that evening glow. Post processing gets rid of it somewhat, but I lose other tones in so doing. What is the best way to deal with the mist?