In practice, circular polarizing filters are easy to use. They are available in a wide variety of diameters to fit most any modern lens and screw onto the thread at the end. Polarizing filters work by only allowing a certain angle of light to pass through. The intricate science behind how filters actually work is well described on this Colorado University website. In simple terms, a circular polarizing filter is rotated so certain wavelengths of light are blocked from entering the lens and hitting the sensor.