SPHERICAL || Each lens is spherical in shape and measures 2" (50mm) in diameter FOCAL LENGTH VARIETY || Converging and diverging focal lengths in 200mm, 300mm and 500mm OPTICALLY WORKED GLASS || Made of high quality, optically worked glass. Highly polished with ground edges GREAT FOR PHYSICS CLASSROOMS || This optically true lens set is excellent for physics classroom demonstrations in optics and light refraction SET OF 6 || Set of six includes 3 double convex lenses and 3 double concave lenses