found at DigiDirect
With a 4x filter factor that reduces exposure by 2 stops, this Haida NanoPro MC Hard Grad ND0.6 Optical Glass Filter - 2 Stop 150x170mm is designed to darken select portions of your image without affecting image sharpness or color reproduction. It features a hard edge in its center that starkly divides the clear section and the darkened section, making this filter ideal for photos with a sharp horizon such as seascapes and elevated urban landscapes.
The NanoPro MC is made of optical glass and features a 2mm thickness compatible with a wide range of holders. Both sides of the filter are treated with several layers of coating, resulting in minimized reflections and increased resistance to scratches. The multi-coated construction also makes it easier to clean water and other debris from the glass surface, suiting it for use in the outdoors.