The HOYA PRO-1 Digital neutral density (ND4) filter reduces the amount of light entering the lens and is ideal for wider apertures or longer exposures. The purpose of standard photographic neutral density filters is to allow the photographer greater flexibility to change the aperture or exposure time, allowing for more control, particularly in extreme circumstances. This is perfect for portraiture to reduce depth of field. Subject appears crisp and clear while the background becomes a soft blur. Also widely used for photographs of waterfalls and other nature scenes to emphasise movement. ND4 reduces amount of light to 25% - absorbs 2 F-stops of light. ND8 reduces amount of light to 12.5% - absorbs 3 F-stops of light. - Digital Multi-Coated Digital multi-coated filters greatly reduce the appearance of lens flare and ghosting caused by reflections. - Black Almite Frame Filters feature a black matte aluminium satin finish almite frame which reduces reflections. - Black Rimmed Glass These filters are equipped with black rimmed glass to reduce the chance of light reflecting off the edge. - Low Profile Frame Ultra thin filter frames to help avoid vignetting on super wide angle lenses are also designed to hold a lens cap. - Knurling Edge Frame These filters are equipped with a straight knurling edge for non-slip, easy attachment and removal. - UV Protected Case Filter cases are UV protected to further lengthen the life of filters.