Hoya Pro ND16 Neutral Density Filter - 77mm ND16 is 4 stops of light or 1/16 of shutter speed. The Hoya Neutral Density filters are a useful filter to have in the lens kit. This filter will reduce the amount of light passing through the lens by a factor of four stops. This filter is primarily used to create a shallower depth of field, allowing the lens to remain at a fast speed. Alternatively, this lens can be used to increase exposure time for long exposure photography.