UV filters protect camera lenses from damage and dirt while also reducing haze. Polarizing filters darken skies, increase saturation, and reduce reflections. They have the biggest impact on water, sky, and color. There are linear and circular polarizing filters. Infrared filters allow infrared photography. ND filters reduce exposure for all wavelengths equally, allowing slower shutter speeds or larger apertures. They are useful for water movement, depth of field, and motion blur. Graduated ND filters transition from neutral density to clear across the frame. Variable ND filters provide multiple densities by rotating polarized layers.