Hoya traces its beginnings back to Tokyo Optical Glass Manufacturing, established in November 1941 by the for Brother s Yamanaka. Optical glass requires highly sophisticated manufacturing technology compared to other types of glass, and at that time it was the most technologically advanced industry. Hoya produces more than 100 different varieties of optical glass, working from a proprietary “recipe book” that contains over 50,000 different ways to manufacture glass. Hoya carefully selects the purest materials from around the globe, and combines them in a multitude of ways to create an endless variety of glass products with optical characteristics that precisely match market needs. Neutral density (ND) filters reduce the amount of light entering the camera, this enables the option to select a longer exposure time than would have been possible. This can then bring life to motion. Also an ND filter enables larger aperture selection, resulting in a shallower depth of field. Either way, this is a very useful filter for use in still or motion photography. The ACCU-ND technology in the Hoya PROND filters yields a truly neutral colour balance that will not add any noticeable colour-cast to your images. The Hoya PROND series is aimed at the still photography and HDSLR video markets. The series provides 9 filters from two stop to 10 stop light reduction.