Elizabeth Grosmann Rung and the Lyle Wells would seem to have little in common. She is a suburbanite from Malverne, while he lives in rural Aquebogue. But both are farmers, working land has been their families for generations, and keeping one of the Long Island's nearly obsolete occupations alive. And both are featured in a new documentary about farmers on the island, "A Farm Picture," which has its first showing in Stony Brook on Saturday. The film was made by Glenn Gebhard a Los Angeles-based documentary filmmaker who was born and raised in Merrick and owns a secong home in Sound Beach, and Mario Congreve. The two previously made a documentary about the Island's baymen, another endangered local occupation. "Doing one on another job in jeopardy seemed natural," Mr. Gebhard said. The script for the film,which is an hour long, was written by Frank Turano, who teaches Long Island environmental history and human ecology at the State University of New York at Stony Brook. It traces the history of farming on the island from the Native American period, when corn sustained the area's inhabitants, to the present when truck farming and grapes have replaced potatoes as the major focuses of agriculture, and continuing development threatens the industry's survival.