With its vast stage, extraordinary technical capabilities, and long roster of star singers, the Met rarely does anything on a small scale. But "Opera by Design," a new exhibition at the Arnold & Marie Schwartz Gallery Met, goes miniature in a grand way, with a display of handmade, intricately detailed set models created by the designers behind the seven new productions premiering next season. The models serve as blueprints for the Met's army of carpenters, painters, and craftspeople and provide a window onto how the collaborative vision of designer and director takes shape.