5-elements Multi-coated Optical Glass with anti-reflection coating Doubles focal length of lenses Manufacturers' Lifetime Warranty Item Includes: Case, Protective Lens Cap, Nwv Direct Micro Fiber Cleaning Cloth 2x (Doubler) 5-element Teleconverter multiplies the focal length of any fine optic it's used with by 2x, maintaining the resolution and contrast at a high level.