Opera in Williamsburg, the innovative opera company that performs two fully-staged operas in Williamsburg each year, will open its doors at 11:45 am so Osher members can observe a working rehearsal that begins at noon. The singers will already have rehearsed the music and the staging before coming to the Kimball Theatre. This rehearsal will be a work session with piano accompaniment, with no costumes and with minimal props, with possible repetitions and with backstage staff moving around. The opera this time will be Mozart's fantasy The Magic Flute (sung in German, with English supertitles and with English dialog.) The finished production, on May 5, 7, and 9, will use lavish fantasy costumes.