Sciencent Double Concave Optical Lense 20 cm Focal Length, 75mm Dia Go to amazon.com Related posts Top 6 best spinning top base: Which is the best one in 2022? FeatureDouble Concave Lnes75mm Diameter20cm Focal LengthSciencent High Quality Glass Lens DescriptionSciencent High Quality Double Concave lens. 75mm Diameter, 20cm Focal Length