John T. Rossi was named vice president of finance and CFO at OmniVision Technologies Inc., a supplier of CMOS CameraChip solutions for high-volume imaging applications. He succeeds H. Gene McCown, who is retiring.   . . .   Candela Corp. announced it has received expanded clearance from the US Food and Drug Administration to market its Smoothbeam diode laser for the noninvasive treatment of wrinkles on the face.