Unless you’re a real amateur film buff, the odds are that you’ve never hard of Sidney N. Laverents. But as filmmakers go, you’d be hard-pressed to find a more influential or prolific amateur. “Now 95, Mr. Laverents is a distinctively American artist: a rec-room tinkerer with the can-do optimism of someone who got through the Depression and found comfort in the suburbs. Following his own whims rather than any cultural movement, he turned himself from a one-man band into a one-man independent movie studio.” This week, 34 years after the release of his award-winning special-effects feature “Multiple SIDosis,” Laverents has earned an L.A. retrospective.