What is a polarizing filter primarily used for in photography?

A polarizing filter is primarily used to reduce reflections from non-metallic surfaces, such as water and glass, which can significantly enhance the clarity of an image. By minimizing these unwanted reflections, the filter allows for a more vivid representation of colors and details in photographs. It effectively darkens skies and increases contrast in landscapes, making the blue of the sky appear deeper and the whites of clouds more pronounced.

In addition to reducing reflections, a polarizing filter enhances color saturation by cutting through haze and preventing glare, which helps bring out the true tones of the scene. This results in more vibrant and visually appealing images, particularly in outdoor photography where natural elements are abundant.

Though enhancing brightness levels and adjusting ISO settings are important aspects of photography, they are not functions of a polarizing filter. Similarly, changing the focal length of a lens pertains to the physical design and capabilities of the lens itself, rather than the effects provided by any type of filter.