Featuring high quality AGC glass from Japan, MRC-8 and water and dust repelling nano coating layers, the Breakthrough Photography x2 is the gold standard filter for the discerning professional photographer. Available in either 3-stop or 6-stop, the x2 ND features a weather-sealed traction frame which makes getting filters on-and-off a whole lot easier. In addition to having professional optical performance, x2 features state-of-the-art multi-resistant coating. Four layers of state-of-the-art MRC are applied to each side of the optical disk, resulting in a total of 8 MRC layers. MRC coatings are structurally harder than the glass itself, which increases durability of the optical surfaces by increasing scratch resistance. Incredibly durable. By design. Each X2 ND filter is CNC machined with very narrow tolerances, and manufactured with an incredibly low threshold for defects and a strict quality control process. The result: each and every x2 ND filter is built to last at least 25 years, if not beyond a human lifetime. Less has never been more. The x1 features a 3.5mm ultra-slim double-threaded Traction frame profile to eliminate vignetting on wide-angle full-frame setups. Why 3.5mm Tests show that the 4mm is the frame width at which point vignetting becomes noticeable on 16mm wide-angle setups on full-frame cameras. But any lower than 3 and lens caps and such don't stay on. At 3.7mm vignetting was entirely eliminated. Double-Threaded & Laser Engraved. x2's 3.5mm frame still accepts all lens caps just fine but also stays below the 3.7mm. Laser engraved lettering in the x2 Traction frame ensure that the lettering won't ever fade or come off even after consistent use. Breakthrough also engraves each and every x2 Traction frame with a unique serial number. When you activate your 25 Year Ironclad Guarantee, Breakthrough associates your x2 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. Weather-sealed durability. If you want to ensure that your lens maintains out-of-box optical performance for as long as possible, Canon, Nikon and Sony recommend protective filters for the purpose of completing a lens weather-seal. Without a filter, the lens is not dust or water resistant, as Canon states on page 2 of their lens user manuals.