B+W 49mm 103 ND 0.9-8X (103M) 66-1066139 Neutral Density Filter with Multi-Resistant Coating (MRC) 0.9 ND - 3 f-stops - 87.5% reduction of light - Transmits 12.5% of the light from the original scene Filter Factor = 8x Multi-Resistant Coating (MRC) 8 layers per side. This filter uses our standard B+W F-Pro filter mount, which has a front accessory thread and is made of brass.