A water lens I built as I explored how to get large lenses for illumination management without busting the budget. It is in essence a tank with perpendicularly cylindrical front and back walls. The cylinder radii are such that both foci are coincident. It is built by appropriately shaping aluminum side walls, then enclosing the tank with thin acrylic sheets (seen here with their protective film still on). You can clearly see the magnification of the Windex bottle behind it. This lens had a focal length around 950 mm. The lens is about 10 x 10 inches.
