In his workshop in Padua, Italy, he discovered that plano-convex and plano-concave lenses worked best—that ... Galileo played with this formula until, by the late fall of 1609, he'd made a ...

A plano-concave lens is a lens with one side being flat and the other side being concave. It is characterized by being thin in the center and thick at the edges, and can make parallel light rays ...