Usage
The polarizing filter is one of the most commonly used filters in photography. Polarizing filters allow only light of a specific vibration level to pass through, while filtering out all other light rays. This filtering reduces reflections on glass and water surfaces or paints. At the same time, they increase color saturation and enhance contrast. Objects behind glass (such as shop windows or car windows) become visible again. In landscape photography, the polarizing filter achieves its maximum effect at an angle of 90 degrees to the sun. For a uniform effect in the image, one should not use a focal length shorter than 35 or 28 mm in full-frame format due to the uneven polarization of daylight.

Functionality
Circular (CPL) and linear polarizing filters operate on the same principle. Optical grids on the filter film ensure that only linear light waves reach the lens, whose orientation matches that of the grid. Unlike a linear polarizing filter, the circular polarizing filter has an additional lambda/4 plate. This plate ensures that the linear light rays created in the polarizing filter are decomposed back into all components and are at a 90-degree angle to each other. At the same time, one component is delayed by a quarter wavelength. Thus, all polarization directions are present behind the filter again, which prevents the autofocus problems that often occur with polarizing filters from happening with circular polarizing filters.