Sigma WR Ceramic Protector (available from 67mm to 105mm) Interchangeable lenses are the most important element of photographic expression, and to the photographer they are a valuable personal asset. To help photographers continue to use for many years the lens systems in which they have invested their time, knowledge, and budgets,SIGMA has developed original lens filters that meet the company's high standards of excellence. In developing its new protective lens filter, SIGMA has leveraged an unprecedented cooperative relationship with a glass manufacturer, resulting in a completely new type of glass called Clear Glass Ceramic. Featuring this advanced material, the SIGMA WR CERAMIC PROTECTOR is a highly reliable filter with outstanding protective capability. With many applications in aerospace and other industries, glass ceramic is an extremely tough type of crystallized glass that serves as the foundation for Clear Glass Ceramic. While featuring the high transmittance required of optical devices, this advanced new material combines greater hardness than chemically strengthened glass and greater flexibility than sapphire crystal glass. These qualities make Clear Glass Ceramic the ideal material for protective lens filters. Highly shock-resistant Clear Glass Ceramic In the chemically strengthened glass used in conventional high-strength protective filters, only the surface is strengthened through chemical processes. In contrast, Clear Glass Ceramic is made with a special heat treatment that precipitates microcrystals of a mineral called spinel evenly throughout, giving the entire filter consistent strength. Combining much greater hardness than chemically strengthened glass and greater flexibility than sapphire crystal glass, Clear Glass Ceramic is the ideal material for protective filters. Clear Glass Ceramic is also resistant to cracking due to small scratches or chips. Since the risk of shattering and producing fragments is reduced, it also offers an enhanced level of safety. Scratch-resistant Clear Glass Ceramic offers a Vickers hardness number of 700HV.* This is a level of hardness much higher than that of chemically strengthened glass, which is used in conventionalhigh-strength protective filters. Moreover, this higher level of hardness helps prevent scratches and chips, which can lead to breakage of the filter. *In the Vickers hardness test, a diamond instrument is pressed onto a material, and the indentation so produced is used to calculate the hardness of the material, which is expressed as a Vickers Pyramid Number (HV). 10 times the strength of a conventional protective filter, 3 times the strength of a chemically hardened glass filter Made with a special process that evenly precipitates microcrystalline spinel throughout the material, Clear Glass Ceramic offers a Vickers hardness number of 700HV. The new SIGMA filter made with Clear Glass Ceramic offers over 10 times the strength of a conventional protective filter and over 3 times the...