Hoya Pro ND32 Neutral Density Filter - 77mm ND filters come in different 'strengths' known as stops of light. 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 five 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.