WORLDS MOST COLOUR NEUTRAL DARK POLARIZER, GUARANTEED: A perfectly flat transmission curve would yield a perfectly colour neutral result, and while there is no such thing as a perfectly neutral CPL filter (contrary to what other filter makers may claim) the X4 CPL is the most colour neutral any CPL filter, guaranteed. WORLDS MOST ADVANCED POLARIZER: The Dark CPL incorporates our X4 CPL film we achieved a gradual transmission decrease from 600nm onward, and instead of spiking uncontrollably near 650nm and far into infrared, the Dark CPL sees very controlled transmission into IR, without the curve spike. Result: Warm and lively images without the typical yellow colour cast. X4 DARK CPL (CIRCULAR POLARIZER) FILTER: The X4 DARK CPL features SCHOTT Superwhite B270 optical glass, which is an ultra clear crown glass. It is produced by melting high purity raw materials and then made using the continuous draw process. The result is excellent transmission in the ultraviolet, visible, and infrared spectrums, and a high surface quality that accepts our state-of-the-art MRC and nanotec coatings exceptionally well. FITMENT: This DARK CPL filter is compatible with all camera lenses with front threads between 46mm up to 105mm. Your lens thread size will be printed underneath your lens cap or written somewhere on the lens barrel. Make sure you order the correct size otherwise it will not fit your lens. 25 YEARS SUPPORT: We stand behind every X4 DARK CPL filter we make with our 25 Year Ironclad Guarantee. Every X4 DARK CPL filter has a unique serial number laser engraved onto the interior frame and you will use that number to activate your warranty. Specs Glass Type - SCHOTT B270 Optical Glass Filter Type - Circular Filter Filter Factor (Light Reduction) - 3 stops, 6 stops, 10 stops Filter Sizes - 49mm, 52mm, 58mm, 62mm, 67mm, 72mm, 77mm, 82mm, 86mm, 95mm, 105mm, Magnetic