"It's magic: Two consumables that are very important when running a laser are the focusing lens and gases used for cutting. …Ophir's new Black Magic focusing lens gives long life. It averages about 600 hours of use compared to roughly 300 hours to 400 hours with ordinary yellow lenses. A high-power laser puts more demand on critical components, such as mirrors and lenses, resulting in higher lens-replacement costs. The black Magic lens has less absorption of the laser beam than standard lenses, especially important with today's high-wattage lasers. This keeps power at the focal point for cutting, not in heating the lens. Black Magic lenses are made from the highest grade of low-absorption zinc selenide, and its proprietary coating is less sensitive to the heating effects of the laser beam. As a result, the usual thermal response of a lens during use, causing the focal length to move, isn't an issue. The focal length of the black magic lens stays constant."