This ND4 filter reduce the amount of light entering the lens so wider apertures can be selected, which is perfect for portraiture to reduce depth of field. Subject appears crisp and clear while the background becomes a soft blur. Also widely used for photographs of waterfalls and other nature scenes to emphasize movement. The ND4 reduces light entering the camera lens by the equivant of 2 stops FEATURES ZR ( Zero Reflection ) Super Multi-Coating This innovative coating will not interfere with any color or light transmission. Reflections are eliminated by allowing light to enter the filter at virtually any angle. This filter will produce superior results and can be used with any type of lens (wide angle to telephoto). Ultra Smooth Surface - Nano Glass Technology Our Nano Glass Technology creates an ultra smooth surface from the finest particles of glass, making it stain and scratch resistant without any effect to the image. Ultra Thin Frame The glass of this filter is set in a precision machined frame and attached using Retainer Ring Mount Technology giving this filter an unsurpassed durability. An ultra thin frame also makes it wide-angle lens compatible.