Fotasy 37mm CPL filter is used to increase color saturation, darken blue skies so white clouds stand out. And eliminate reflections from non-metallic surfaces like glass or water. It will also reduce the softness in scenery caused by atmospheric haze. Light rays which are reflected by any surface can become polarized so polarizing filters are used to select which light rays enter your camera lens. CIRCULAR PL filters allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colors to become more saturated and appear clearer with better contrast. This effect is often used to increase the contrast and saturation in blue skies and white clouds.