Hoya 52mm NDx400 HMC FilterThe Hoya 52mm NDx400 HMC Filter is a solid neutral density filter that enables a 9 stop increase in exposure length. The optical 2. 7 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily.