The NiSi Explorer Collection 100x150mm Nano Ir Reverse Graduated Neutral Density Filter - GND8 (0.9) - 3 Stop is part of our Explorer Series for made for adventure. The filters feature a special glass hardening process that makes them double the strength of typical glass filter. The Explorer series are much less prone to accidental breakage and perfect for active photographers. Double the Strength of Typical Glass Filter B270 Glass Ir Layers for Accurate Color Low Reflection Nano Coating Compatible with 100mm Filter Holder systemsThe NiSi Explorer Collection 100x150mm Nano Ir Reverse Graduated Neutral Density Filter - GND8 (0.9) - 3 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. Reverse edged GNDs are similar to hard-edged GNDs except that the darkest part of the filter is at the transition point.