Police were searching for a smooth-talking convicted rapist who videotaped a women’s self-defense lecture while posing as a film maker. Ruth Brown, volunteer coordinator for San Francisco Women Against Rape, said she was shocked to learn she had befriended David Earl Babb, who is free on appeal of a 1978 rape conviction and 15-year prison term in Florida. Babb also faces sexual assault charges there and in Los Angeles and San Francisco. Brown said she got a phone call in early May from a man identifying himself as a film maker, who said the rape of a friend had spurred his interest in producing a 30-minute film about rape-prevention. Babb later filmed a presentation about self-defense before about 20 college women.