Formatt Hitech Limited HT100NDRG0.6 100x125MM (4-Inch x 5-Inch) Neutral Density Reverse Graduated 0.6 The filter is also available in 85mm, 150mm and 165mm sizes. Hitech filters are made from the highest quality 1.5mm optical resin. A 100mm (4-Inch) x 150mm (6-Inch) version is also available for added flexibility.