Optical illusions of the photgraphic kind make up the Art Institute's new exhibit "Sight Unseen: Photographs From the Permanent Collection," on view through March 13. The museum is open 10:30 to 4:30 Monday, Wednesday, Thursday, and Friday; 10:30 to 8 Tuesday; 10 to 5 Saturday; and noon to 5 Sunday. Admission is voluntary, but $6.50 is suggested for adults, $3.25 for students, seniors and children. Tuesday admission is free. For more info call 433-3515.