In antiquity, we see examples of magnifying crystals formed into a biconvex shape as early ... Many smartphones today still use a three-element lens system, heavily inspired by the Cooke triplet.

or lenses that are flat on one side. Biconvex lenses can be constructed by gluing two planoconvex lenses back to back, which is done with an acrylic glue, in this case Acrifix adhesive.