Fotodiox Pro 145mm Neutral Density 4 (2-Stop) Filter - Pro1 Multi-Coated ND4 Filter (works with WonderPana 145 & 66 Systems) Premium Grade Optical Glass Filter 145mm x 1mm Standard Thread, both in the front and rear Premium Grade Anodized Aluminum Filter Ring Other Available 145mm Filters include CPL, ND4, ND8, ND16 & ND32 Filters 24 Month Manufacturer Warranty