Made in japan.
Hoya incorporated magic coatings in these HD (Heavy-duty) filters that are resistant to scratches, dirt and finger prints. Any oil stain on the glass can be removed effortlessly, unlike other filters where stains just stick to the glass like glue.
Hoya HD filter uses specially hardened glass (4 times the breaking strength in ansi standardized testing) that is far more resistant to breakage than other optical glasses. Hoya HD polarizer uses special polarizing material that gives photographer 1 stop of light to come through. This is amazing feat considering most polarizers will cripple or slow down photographers with 2 stops of light.
Designed exclusively for digital cameras, this multi-coated Hoya HD digital circular polarizer allows you to remove unwanted reflections from non-metallic surfaces such as water, stone, glass etc. 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. They also enhance 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. Hoya polarizing filters do not affect the overall color balance of a shot.