EISCO 6pc Optical Lens Set, 3" - 200mm, 300mm, 500mm Focal Lengths - 3 Double Convex & 3 Double Concave, 3" (75mm) Diameter Lenses - Optically True Glass - Ground, Beveled Edges
Optical Glass Lens Set, 6 Lenses - 3 Double Convex, 3 Double Concave - 75mm Diameter - 20, 30, 50cm Focal Lengths
(3) Double Concave -20,30,50cm Focal Length, (3) Double Convex - 20,30,50cm Focal Length
This lens set is perfect for doing optical experiments comparing focal lengths and convex vs. concave lenses.