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Polarization – the When, How, Why of it

Posted on: June 11, 2017 at 5:27 am

If you’ve ever used a polarizer, or a CPL filter, you already know a little about polarization of light. Still, most people just know that it cuts out reflections from certain surfaces. KAPA students learn this in detail. Here’s a gist of it.

Light particles tend to scatter in all directions from any one point, think of a bulb in a room…certain reflective surfaces bounce them, back again in all directions opposite to the source, say for example a mirror or polished metal. However, semi-transparent surfaces let some of the light go through and some of it is reflected back, say for example a car windshield. The light reflected back by these semi transparent surfaces has a definitive direction to it – this is what we called polarized light. To understand this in simpler terms, it is the reflections you see on glass windows, windshields, shiny surfaces, glossy magazine covers and such. In most situations, these reflections are undesirable and a CPL filter is used to cut out this polarized light. Its totally a matter of what you want as end result…

Take for example this photograph of actress Riya Sen, shot by Karthik Srinivasan on SONY Alpha 99 with 1 135mm lensĀ (1/125sec, ISO-100, f/4). Notice the reflections on the swimming pool right behind the model. This is polarized light. To use a CPL filter would have cut off this reflection, giving the water an even tone. But in this case, the polarized light has created a nice contrast and relief from the cyan tone, so it was left as is. Again, its totally a matter of choice what you want out of your photograph…try using a polarizer on different semi transparent surfaces to know the difference.