The battle between the Autobots (the good robots) and the Decepticons (the evil ones) continues in “Dark of the Moon,” the latest in the “Tranformers” franchise from the director Michael Bay. This installment brings more destruction, more robots and one powerful cinematic weapon: 3-D. Another important element of the film is the setting — downtown Chicago — of a third-act battle sequence. A typical Michael Bay frame is packed with activity, and the one here is no different, with the technology, setting and action all vying for attention. Mr. Bay and Scott Farrar, the film’s visual effects supervisor and second-unit director, explained what went into the shot. MEKADO MURPHY