The Sigma 67mm WR Ceramic Protector Filter is a clear filter designed to guard the front of a lens from impacts, and is characterized by its one of a kind durable construction, which protects from scratching, and other elements. Designed with a clear glass ceramic substrate, this filter combines a high 99.76% transmittance value with greater hardness than chemically-strengthened glass, as well as greater flexibility than sapphire crystal glass. The filter's design is scratch and shock-resistant to handle a variety of impacts while shooting. A water-repellent coating is also applied to resist water droplets and fingerprints, as well as static electricity from collecting dust particles. Sigma's 67mm WR Protector Filter's design also helps to maintain the lens' inherent image quality while providing a high degree of protection. Its unique construction has a Vickers hardness number of 700HV, making it both shock and scratch-resistant. This hardness also decreases the likelihood of scratching or chipping that can lead to the filter shattering. Instead of only the surface structure being hardened, the clear glass ceramic involves a heat treatment process which creates microcrystals of a mineral called "spinel" in order to achieve even, consistent strength across the entire filter. This strength also allows the design of the filter to be thin and lightweight. A water-repellent (WR) coating prevents water and oil from adhering to the filter surface, while helping to minimize ghosting and flare. The coating reflects 0.24% of light, giving an overall transmittance value of 99.76%. The acrylic case (included) protects the filter when it is not in use and is designed to prevent accidental, unwanted opening.
