Product Description Formatt Hitech 150x170mm (6"x6.69") Neutral Density Reverse Grad 0.6 (2 Stops) for Lee SW 150 Holder Systems compatible with all 150mm holder systems. From the Manufacturer About Formatt-HitechFormatt-Hitech filters are designed and manufactured in the UK. Formatt-Hitech takes a scientific approach to light modification and designs filters using advanced spectrography to manufacture the most evenly balanced and well matched filters in the world. By using a spectrograph, Formatt-Hitech designs filters of varying density that modify light in the same way, just to varying degrees of intensity. So you can switch from a 0.3ND to a 1.2ND without changing the look of your project. Strict quality standards also mean that if you break a filter today, we can replace it tomorrow with a filter virtually identical across the frequency spectrum. So your 5 piece matched set of ND filters will always remain a matched set of filters, even if one should break and need replacing.TechnologyFormatt-Hitech use our award winning and exclusive Absorbing Cell Technology process to dye the resin. The Absorbing Cell Technology process absorbs dye into each cell of the resin rather than coating onto it, ensuring that the affect is applied consistently across the filter. This means that each Formatt filter can be consistently replicated time after time. The densities and formulation of the dying process are strictly computer controlled, creating the most accurate filter reproduction in the world.Materials ScienceFormatt-Hitech's resin was designed specifically for use as a lens material and has an index of refraction nearly identical to the finest optical glass. Formatt-Hitech's resin has the highest scratch resistance of any optical plastic and it is resistant to most solvents, chemicals, aging and material fatigue. Meaning that your resin filter investment will provide many years of good service. Formatt-Hitech's resin is completely transparent to the visible spectrum and opaque to ultraviolet light to eliminate UV contamination on your digital sensor.Choosing a Filter SystemUsing a filter holder rather than a circular screw-in filter allows you to make a single filter purchase that is used across a variety of lenses. 85mm filters are an excellent choice for small mirrorless camera systems such as Leica M and Micro Four Thirds systems, or DSLR users with small lenses. The 100mm system is an excellent all-round choice. 100mm filters are popular for DSLR photographers and DSLR cinematographers using larger, more expensive lenses. Typically, most solid filters are square. Graduated filters are rectangular to allow for vertical adjustment of the horizon.