Filters: The Polarizer

The polarizer is one of most universally useful filters. We could go into the science of how it works, but we won’t. (If you’re interested read up on this fascinating topic on the Physics Classroom or on Cambridge in Colour.) Much rather let’s talk about what it does.

Light reflected from a flat surface is polarized and the polarizer allows us to filter out this reflection to a greater or lesser degree. Typical flat surfaces that we meet in photography are water, glass, metal and the sky. That is, the sky is not exactly flat and as we will see this greatly influences the effect of the polarizer on it.

As reflections are enhanced or decreased we not only change what we see in the image but can also increase contrast or intensify colours.

Here are a few examples.

In the above two pictures the polarizer emphasized and then almost entirely eliminated the reflection in the dark marble. The two images were taken with the same settings you they demonstrate another characteristic of polarizers: depending on how you turn them they absorb more or less light – anything between 2/3 of a stop to a stop and a half.

This is one of the most widespread uses of the polarizer: making the sky look darker. Remember: it works best when the image you’re taking is at a right angle from the Sun. When the Sun is behind you or in front of you, you won’t really see a difference. As you can see, by rotating the polarizer it was not only the sky that got darker, but the windows of the building, as well.

And because the sky is not flat (and neither is the Earth) the polarizer can wreak havoc with your image, like in the one below, giving the appearance of your shot being unevenly lit. Fortunately, with polarizers WYSIWYG, so you will always see in your viewfinder if you have a problem.

20150302-Polarizer filter test [exposureworks glaszlo.com London DSLR course]-5D3_1234

In the video below you have two sets of images demonstrating these points. The second set show you how a polarizer works with a curved surface.

Enjoy your puddles, oceans, windows, screens, polished marbles and all the flat surfaces that surround you!