Camelot,” the 1960 musical based on the Arthurian legend — this time rewritten by Aaron Sorkin — at the Vivian Beaumont in Lincoln Center. All around the theater are long tables shrouded in black cloth where tech people are writing on notepads, flipping switches and speaking quietly into headsets, their eyes never leaving the 4,000-squarefoot stage suspended above the orchestra pit like a massive UFO. Actors in medieval costumes are talking in small groups, choreographers are nervously pacing, a producer is heatedly whispering, and Bartlett Sher, 64, the director, is standing in an aisle near the back, watching silently, like a captain on the prow of his ship.