Understanding and using a polarizing filter for photography

Question: What is “polarization”?
Answer: Polarization is used to describe the direction of the electric field generated by the propagation of electromagnetic waves. Polarization can be linear or circular. Linear polarization means the electric field generated by the wave is oriented in a single direction but in circular polarization, the electric field rotates as the waves propagate.

Question: Why use it in photography?
Answer: Sunlight that is reflected from non metallic surfaces is polarized. It would mean reflections from clouds, surface of the water, glass such as windscreen of cars and surfaces of vegetation are all polarized light. Using a polarizing filter, we can remove such reflections. However do remember that it will only work on reflections from non-metallic surfaces. Another point to note is the effect of using a polarizing filter cannot be replicated in photo editing software.

Question: What is a circular polarizing filter?
Answer: A circular polarizing filter actually consists of 2 optical elements but only 1 filter. The front element, which is facing the object being photographed, is a linear filter. This front element is what produces the effect of the polarizer making the sky darker and removes the reflections. The back element is a quarter-wave plate which has the effect of circularly polarizing the light coming out from the other side. Both linear and circular polarizing filters produce the same effect.

Question: Why do we have to use a circular polarizing filter for our modern day cameras?
Answer: For the reasons of correction operation of the auto focusing and light sensors, we have to use a circular polarizing filter. Linearly polarized light interferes with these sensors.

Question: What is the best way to use a polarizing filter?
Answer: There is no best way to use this filter. Since the effect changes when the front element is rotated, the photographer can choose the desired effect. For the most absorption of reflection, point your lens perpendicular (90 degrees) to the sun.