Fotodiox Pro 6.6" x8.6" Rectangular 0.9 (3 Stops) Hard Edge Graduated Gray, Neutral Density (ND) filter for WonderPana 66 System Holder Premium Grade Optical Polycarbonate Filter High Quality, Super Thick, Multi-Coated Graduated ND4 Filter Practically Unbreakable and are Guaranteed Spectrally Neutral 24 Month Manufacture Warranty