The hoya 67mm hmc ndx4 filter reduces the amount of light entering the lens by 2 fstops allowing wider apertures to be selected which is perfect for portraiture to reduce depth of field subject appears crisp and clear while the background becomes a soft blur alternatively the nd4 filter can be used to allow longer shutter exposures than would otherwise be possible and is widely used for subjects such as waterfalls and other nature scenes to blur the moving elements and emphasize the moveme