The Hoya 49mm NDx400 HMC Filter has a 9-stop light reduction equal to an ND optical density of approx. 2.7.Neutral density filters are designed to reduce the amount of light entering your camera lens and should not have any other effect on the image. Reducing the amount of light allows for the use of wider apertures or slower shutter speeds for creative and dramatic effect in bright lighting conditions.HMC (Hoya Multi Coated)These popular filters are renowned for their ability to minimise reflection at the filter surfaces which reduces flare and ghosting. The result is an average light transmission of over 97%, giving sharp contrast and well balanced colour. HOYA HMC filters are recommended for enhancing the performance of today's multi coated lenses.*This filter is NOT suitable for solar photography. DO NOT look at the sun through this filter, eye damage will occur.Specs:Type: Solid neutral densityDensity: 2.7 (9 stop)Multi-Coated: Yes; HMCEffect: Permits an increased exposureConstruction: Optical glass and aluminium filter ring