Brian De Palma first used the Steadicam, with Mr. Brown as an operator, in “Blow Out” (1981) for the opening sequence, an elaborate horror movie parody in which a slasher attacks coeds. “Choreographing the shot, getting the psychopath to hold his knife up in front of the mirror at the right time — it was a kind of joyful evening,” Mr. De Palma said by telephone. He went on to use the Steadicam in many films, including “Raising Cain” and “Carlito’s Way,” showing in the Film Society series.

For Mr. Brown, who taught himself filmmaking, movies came after a folk-singing career (as part of the duo Brown & Dana) and a stint selling Volkswagens. He found himself working in commercials at a time when the only way to create smooth camera motion was to put the camera on a dolly, in a camera car or on a crane. He was pained by the unwieldy setup of a 12-pound camera on an 800-pound dolly.

“The sight of that pinheaded little camera on that huge dolly and the attendant difficulties of schlepping it around on pickup trucks and laying my paltry rails here and there outdoors really was so absurd,” Mr. Brown said. He wanted to isolate the camera from the motions of the person controlling it — the kind that cause hand-held shots to appear shaky.

The key ingredients were a gimbal, which came from Mr. Brown’s sailing experience; counterweights, to give the camera stability; an articulated arm — an idea he got from a motel desk lamp — attached to a harness that a camera operator could wear; and a way to see through the lens. He originally used a fiber-optic viewer intended for medical examinations.

In a sense, Mr. Brown had realized a dream of filmmakers and theorists who treasured camera motion; it’s hard not to wonder what Max Ophuls or André Bazin would have made of the Steadicam. “Abel Gance — he was fabulous at moving the camera,” Mr. Brown said, referring to the director of “Napoleon,” the 1927 silent classic. “He did extraordinary things, but he didn’t have this tool for stabilizing. I would have loved to have shown up on his set.”

In the earliest Steadicam movies, Mr. Brown operated the apparatus himself, and he continued to do so for three decades. Now, he said, Steadicam operators make expert shots for TV news broadcasts and from the sidelines of sports like football and soccer.

Robert Elswit, the cinematographer on two Paul Thomas Anderson movies in the Film Society series, “Boogie Nights” and “Magnolia,” considers the Steadicam essential. “To me, it’s not a specialty item,” he said. “It’s usually there all the time.” The results, he added, are sometimes “not even necessarily recognizable as a Steadicam shot. You just use it to get something done in a simple way.”

Mr. De Palma cautioned that the Steadicam is only a tool, a way of showing the viewer an environment. “You need a lot of sophisticated technicians to pull off a really good Steadicam shot, and that sort of comes with making movies in the studio system in Hollywood,” he said.

Digital cameras make it less complicated to light scenes, he noted, and the equipment weighs less, leading to what he sees as the Steadicam’s overuse. “You see an abundance of Steadicam shots that are completely ridiculous,” Mr. De Palma said. “God knows, in television, they do it all the time. People are always walking and talking and going around corners.”