What is polarized light
We see and photograph reflections of light from the surfaces surround us. If objects did not reflect light we would not see them. Upon reflection, however, the quality of the light may change with undesirable side effects for photography. Before it reflects from a surface, light wave moves in all directions very much like a pipe cleaner with its bristles coming out in all directions. When it reflects from a surface, depending on the angle, reflective surface qualities, our angle of observation, the part of all of the light may become polarized. A polarized light wave no longer moves in all directions but in one direction much like a recording tape, flat.
What is a polarizing filter
When polarized light hits the camera lens, and consequently the film or the digital sensor, it records only as a shiny reflection and we do not see the surface from which it reflects. In order to see the surface, we need to remove the polarized light so the non-polarized light could record an image of the actual surface, say water or display window. A polarizing filter performs this task depending on many factors. By rotating it, we bring its “light grill” so to speak perpendicular to the polarized light direction and it cannot pass through the filter, the lens and record the reflection on the photograph. To visualize the concept, hold your hand out with fingers close to each other but not touching, call this the polarizer. Then, take a crisp dollar bill, call it the polarized light, and slide it through your fingers. Now, hold the angle of the dollar bill and rotate your hand, presto, you have created a “dollar polarizer.”
How does it work
Now, this is how it works. But it does not work all the time and at all angles. First, it only works for light that reflects off nonmetallic surfaces. It is not going to do much to remove the reflections from the stainless-steel kitchen sink. Second, it depends on the angle of the light hitting the surface. Light gets polarized when it hits a surface at a particular angle. (I am not a physicist, so I am probably sticking my neck out here, but I think that angle is 26 degrees.) The effect of a polarizing filter depends on the angle of rotation with respect to the camera lens, thus, the incoming light. If the angle is perfect, it may totally remove the reflection and you could see the fish swimming under water. Otherwise, the effect will be partial or even nonexistent.
How to use it
A polarizing filter is very useful in many photographic situations but it really comes to its own in outdoor, nature, and landscape photography where lighting cannot be controlled. Under outdoor lighting practically everything reflects the blue sky and thus lose part of their color depth. A polarizer may remove the reflections on the leaves and make the foliage really show its true color. Reflections on water could be very dramatic if planned or they could be very distracting if polarized light interferes with the photograph. Again, a polarizing filter could remove some or all of the unwanted reflections.
Perhaps, the most common use of a polarizing lens is to deepen the color of bright blue sky, like those you would see on a crisp day. Here, there is literally a “rule of thumb” to use to figure out where the maximum polarizing will occur in the blue sky. As you stand outdoors, under the big blue sky, hold your hand out with only the index finger and the thumb extended. Now, make the index finger and the thumb form a right angle as if you are imitating holding a gun and point your thumb at the sun. Now, when your rotate your hand around the axis of your thumb, your index finger will draw an arc in the sky where maximum polarizing effect will show. The effect will be quite dramatic if the sky happened to have a few decorative white clouds against the blue sky.
May your light always come from the optimum angle.
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