OmniVision Technologies Inc., a Sunnyvale, Calif., maker of single-chip CMOS image sensors for consumer and commercial applications, has named board member Dwight Steffensen chairman of its audit committee. Steffensen is also a board member at Synnex Corp., an information technology supply chain services company. He was previously chairman and CEO of Merisel Inc., president and COO of Bergen Brunswig Corp. and president and CEO of Synergex until it merged with Bergen Brunswig. He holds a BA degree in economics from Stanford University and is a certified public accountant.    . . .    Gil Varnell, CEO and president of Nikon Research Corp. of America (NRCA), a subsidiary of Nikon Corp., announced he will retire from the company this month. Varnell has worked at Nikon subsidiaries for the last twenty years. Prior to Nikon, he spent 16 years at Texas Instruments in semiconductor R&D labs and later in the Government Electronics Front End. Varnell will be succeeded by Tom Novak, currently senior vice president of Instrument Design and Research at NRCA.