ORIGINAL ARK II ND400 (Reduced exposure grade 9 stops Material Optical glass) Athabasca ARK II ND400 Athabasca ARK ND filters are made of German Schott B270 optical glass. The use of Schott optical glass gives our square filters excellent properties of chemical resistance, high temperature resistance, and abrasion resistance. With an ultra-thin, noble metal multi-coating, Athabasca square filters are with low reflection and able to avoid color differences while also good at reducing light steady. ND (Neutral Density) filters are half neutral density and half clear. As the limited latitude of digital cameras cannot allow for shooting environments with strong light/dark ratios, GND filters are often used to balance the light contrast between strong and weak light. ND(Neutral Density) filters are used to reduce the amount of light entering the lends without effecting the image colors. ND filters are one of an important tool to reduce light, with a ND filter, photographers are able to capture an image with large aperture and shallow depth of field under strong sunlight, and it can attain long-time exposure too. Material: * German Schott optical glass Coating: * Water repellent * Stain resistant * Scratch resistant * Nano coating * Double side anti-reflective film Technology: * Low reflection and light reducing layer Thickness:2mm Installation methods: plug-in filter ND 400: 0.25%(1/400) light is allowed in or 99.75% light is blocked out.t.