ZoMei 49mm Ultra Slim ND2-ND400 Fader Variable Neutral Density Adjustable Lens Filter Ultra Slim ND Filter Optical Glass Double anti-reflective coating, only 7mm thickness ultra thin frame Allows for variable light reduction from between 2-8 stops; protect your lens from dust and scratches Decrease the depth of field by using wider apertures, which helps separate subjects from their background Allows the use of slow shutter speeds, with high speed films or digital cameras, to record movement/image blur in subjects such as waterfalls, clouds or any fast moving subject To avoid vignetting at wide angle lens, this filter has a special front lens, the diameter of the front lens is larger than that of the rear lens