This is the Cokin Z-PRO 164 Circular Polarizing Filter.
Light rays which are reflected become polarized. Polarizing filters are used to select which light rays enter your camera lens. They can remove unwanted reflections from non-metallic surfaces such as water or glass and also saturate colors providing better contrast. The effect can be seen through the viewfinder and changed by rotating the filter.
The Z-PRO Series is recommended for focal lengths of 20mm onwards (in the 35mm format).
Note:
Circular polarizers are specifically designed for use with auto-focus SLR cameras (they will also work on manual systems and video cameras without problems).
This filter eliminates ultraviolet rays from outdoor shots as well as polarizing the light to remove reflections and increase color saturation without affecting the overall color balance
Can dramatically enhance a blue sky and make the clouds more prominent
Used best at right angle to the sun
Effective with cameras that use beam splitters in the path of the TTL light meter and with AF cameras
2x filter factor reduces exposure by 1 stop
Constructed from optical glass for clarity and color fidelity
UPC: 085831708523