To understand how a circular polarizer filter works you will need to understand how light behaves when it gets reflected off a surface, whether metallic or otherwise. I shall not delve too much into the technical side of things, but very briefly this is a refresher course of the chapter on Light that some of you might have studied in school.
Light coming from any source (and one that is not reflected) is unpolarized, meaning, the waves of light move in all directions. When light bounces off a surface which is metallic it is usually, again, scattered in a number of directions. However, when light bounces off a non-metallic surface such as water or suspended particles in the air, it becomes polarized. Polarization essentially means light waves are vibrating in a single direction. In the case of non-metallic surfaces that vibration is usually parallel to the surface from which light is reflected off. This is the reason why when looking down over water you can see nothing more than glare.
From time to time we all complain that the light isn’t right, it’s diffused. Shooting on a bright day we can see haze in the final images that affect the color saturation. At other times, reflections coming off windows or other shiny surfaces such as water, cars etc. creates unwanted blown out highlights in the images. Now you know why all of these happens. A circular polarizer can take care of all these. To understand how this is possible you need to look at how a circular polarizer is made.
A circular polarizer is actually a thin piece of optical accessory that is made by compressing two pieces of glass with a layer of Polaroid in between. The Polaroid layer has millions of molecules inside which are oriented in a particular direction. Polaroid filters are designed to stop light that is vibrating in different directions from passing through and allowing instead only one wavelength, which is parallel to the orientation in which the molecules inside the Polaroid layer are, to pass through. This immediately cuts down on the amount of glare by preventing the unpolarized light waves from entering inside the lens. Turning the polarizer actually changes the orientation of the molecules with it. This allows you to dial in the right amount of polarization.
A circular polarizer filter is a landscape photographer’s best friend because it helps to cut down on haze, glares and reflections. With unpolarized light, light waves are scattered in all directions resulting in glares and reflections due to which details are lost. Colors become unsaturated. With circular polarizers unpolarized light waves are cut and only polarized light reaches the sensor. Polarizers have the most awe-inspiring effect on the sky. Blue sky becomes vibrant raising your images to a completely different level. Often after a vacation you have complained that the images had come out dull, devoid of colors although you had been shooting on bright days. This was because of scattered unpolarized light. Had you used a polarizing filter you would have been able to shoot images that are much more vibrant.
One thing you need to remember is that these Circular Polarizer filter all have different radius to fit different sized lenses, so make sure you get the size that fits your lens. To find out more about filters check out our Using Lens Filters article.