NiSi 150mm Aluminum Square Filter Holder Specially Sigma 20mm 1:1.4 DG Lens 360 Degree Rotation,Without Vignetting Design NiSi 150mm Aluminum Square Filter Holder Specially for SIGMA 20mm 1:1.4 DG Lens Fast installation design,360 Degree Rotation,Without Vignetting Design NiSi Exclusive Two Patents 150mm Filter Holder consist of lens mount clamp foundation and filter installation system.Ergonomic design make Lens mount clamp fixed on the lenses quickly. It's made from aviation-grade aluminum with single element processed by CNC Machine. With matte black frosted finish on the surface. All of screw accessory are made of copper and with black nickel plating.Its durable and can reduce the influence of stray light on the imaging.