The NiSi 100x150mm Nano IR Reverse Graduated Neutral Density Filter ? ND4 (0.6) ? 2 Stop is a rectangular filter that helps to darken specific areas of an image, such as bright skies while allowing for a normal, unaffected exposure in the other regions of the image. The filter is densest at the edge and tapers to clear by the middle, with a hard-edged line of transition between the dense and clear areas. Hard-edged GNDs have a sudden transition from dark to clear. This type of filter is most appropriate for scenes which have a sudden transition from the foreground to the sky. Most commonly, this would include landscapes with no elements protruding above the horizon such as a seascape looking toward the open ocean. They can be used shooting into the direct light where a sharp transition is needed. When used shooting away from the light, they can produce very moody and dramatic skies. Avoid using them where elements protrude above the horizon since those elements will appear very dark above the transition line in your image.NiSi GND filters do not affect the coloration of the image, offer a true to life color and are made from high-quality optical glass (not resin) with nano coating to prevent losing any single bit of detail. By using neutral density filter the camera is vulnerable to infrared light which will cast the unwanted red color to the photos when shooting at a small aperture. NiSi GND filters have an infrared protection coating layer to eliminate the infrared light through the lens to bring back the natural true to life color.