Here's a lot of 12 bioconvex optical lens. The glass feels dense and heavy for it’s size. A single lens weighs in at 10.2 ounces on a digital postal scale and measures 3 3/8 inches in diameter and approx 1 inch thick. Used condition minor scratches and/or small chipped edges as/is for parts projects repurposing or repair. Great for parts or repair, teaching, sculpture, display, crafts or steam punk. We don’t know their specific use; most likely they were used for telescope or projection pieces. Powerful and clear magnification. Great for teaching and demonstration of the properties of light reflection and refraction.