DeMarinis, author of five books of fiction, is this year's winner of the Drue Heinz Literature Prize. In his story ``The Smile of a Turtle,'' an archetypical salesman is selling a fisheye lens for a front door peeper. The lens distorts vision``puts a bend in the world''and this narrowed vision is characteristic of DeMarinis's stories; his landscapes as well as his characters are stretched, flattened. DeMarinis is generous with external detailsthe clothes his people wear, the cars and trucks they drive, the houses they inhabit, all the props of their empty livesand he writes with verve and authority. His stories are often very funny but they are also sad and empty, as sad and empty as his characters. Marcia Tager, Tenafly, N.J.