Circular Polarizing (CPL) Filter — Compatible with Pentax HD PENTAX-D FA 21mm f/2.4ED Limited DC WR Lens

Constructed with an ultra-slim aluminum frame to prevent vignetting while still allowing smooth rotation for level adjustments. A nonslip upper rim makes installation, rotation and removal quick and secure. The glass carries double sided, multi-layered coatings and is anti-oil, anti-dust, anti-soil, scratch & water resistant. This circular CPL removes unwanted reflections from non-metallic surfaces like water and glass and boosts color and contrast. Commonly used to deepen blues and increase saturation in skies and clouds, it also cuts haze in distant landscapes for richer, more vivid tones. The filter works by arranging and filtering directionally polarized light perpendicularly to the reflected light, permitting absorption of much of the reflected light — producing its strongest effect when used at a 90° angle from the sun.