WORLDS MOST COLOR NEUTRAL POLARIZER, GUARANTEED: A perfectly flat transmission curve would yield a perfectly color 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 color neutral any CPL filter, guaranteed. | WORLDS MOST ADVANCED POLARIZER: All commercially available CPL filters exhibit a yellow cast due to a gradual transmission increase starting around 600nm and then spiking at 650nm onward into IR. With 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 X4 CPL sees very controlled transmission into IR, without the curve spike. Result: Warm and lively images without the apparent colorcast. | X4 CPL (CIRCULAR POLARIZER) FILTER: The X4 CPL features SCHOTT Superwhite B270(R) 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(R) coatings exceptionally well. | FITMENT: This CPL filter is compatible with all 43mm camera lenses. 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 CPL filter we make with our 25 Year Ironclad Guarantee. Every X4 CPL filter has a unique serial number laser engraved onto the interior frame. When you activate your 25 Year Ironclad Guarantee, we assign this serial number to you, so any future discussions on this unique filter are tracked, issues recorded and all that stuff which goes into future product design.