Set of Six Optically True Concave & Convex Lenses 50mm Diameter, 200-500mm Focal Lengths High quality, optically true lens. Made of highly polished, quality glass. Spherical with ground edges. Designed for educational purpose and science classroom demonstrations in optics and light physics. Each lens measures 2" (50mm) in diameter. Set includes each a concave and convex lens in 200mm, 300mm and 500mm focal lengths. Eisco Labs proudly manufactures its own products using state-of-the-art equipment, and following the highest standards of quality control. Each product is carefully designed by a team of laboratory professionals and experienced engineers with quality and durability in mind. They are manufactured with only the highest grade, raw materials and according to international quality standards to ensure that they can withstand use in even the toughest laboratory environments.