MINNEAPOLIS – For much of the 20th century, going to the movies meant walking to a single-screen neighborhood theater, where the light from a projector passed through strips of celluloid. Jeffrey Eisentraut loved that experience so much when he was growing up that he eventually moved to southern Illinois to run three historic theaters: the Orpheum in Hillsboro, the Canna in Gillespie and the Roseland in Pana. But now Eisentraut and other independent operators are under siege.

The villain is technology. The movie studios are rapidly replacing traditional reels of celluloid film with hard drives that are cheaper for them to ship and compatible with lucrative 3-D technology. Hollywood says that the digital conversion will benefit moviegoers with consistently bright images and state-of-the-art sound. But in the next few months, exhibitors who don’t purchase expensive new digital projectors may be forced out of business.

Since the first flicker of a nickelodeon, movie-theater owners have invested in many upgrades, from stereo sound to stadium seating, even while losing large portions of their audience to television, home video and the Internet. But the cost of the digital conversion is unprecedented: about $50,000 per auditorium.

Most of the big theater chains have already converted all their theaters. The Landmark chain of art-house theaters will be completely digital by the end of the year. But smaller operators are checking their bank accounts — and their calendars.

Steve Bloomer, who runs the Skyview Drive-in in Belleville, Ill., says he’s been busily consulting with his lender because studios such as family-film specialist Disney will stop producing celluloid reels by next spring. Most of America’s 400 remaining drive-ins are seasonal operations with small profit margins, and Bloomer estimates that a quarter of them will close forever instead of buying the new digital projectors.

Bloomer noted that when he wanted to screen “The Rocky Horror Picture Show” for last year’s Halloween marathon, he discovered that there were only five physical prints of the movie available to theaters. As with most old titles, hundreds of copies had been destroyed to clear space on the distributors’ shelves. So sometime in the near future, theaters that do not convert to digital will not even have the option to show classic movies.

A more pressing deadline is Sept. 30, the last date for exhibitors to join the studios’ “virtual print fee,” or VPF, program. That program reimburses theater owners if they agree to play a certain number of new digital releases per year. Harman Moseley has joined the program and converted all the auditoriums at his St. Louis-area cinemas because he’s enthusiastic about the new technology.

“I miss the whirring of film in the booth,” he said, “but from a projectionist’s point of view, digital is a dream come true. You get uniform, bright white light and crisply defined edges from top to bottom and from side to side. It’s a gigantic leap toward creating a uniform standard of exhibition.”

Moseley added that converting to digital allows him to screen musical performances, video-game tournaments and teleconferences at times when the movie business is slow.

Brian Ross, the co-owner and manager of the single-screen Hi-Pointe in St. Louis, says that converting to digital was a business necessity. Unlike the nearby Tivoli, he intends to keep a reel system handy for special events, such as last year’s screening of a new print of Alfred Hitchcock’s “The Birds.”

Many operators of single-screen theaters are unable — or unwilling — to participate in the VPF program.

Sandra Sinnett, whose family has run the 101-year-old Senate theater in Elsberry, Mo., since 1974, says that the studios want to dictate what films she’ll book. “We won’t show R-rated movies,” she said.

Sinnett says that she and her husband, Robert, have decided to use their life savings to pay for a digital projector because the townspeople need the theater and pitched in to rebuild it after a 2011 fire.

“Most of our customers are farmers who are going through a tough time,” she said. “Last week we had a busload of people who came 50 miles from Vandalia, Mo., because their local theater had closed.”

Eisentraut said that his single-screen Roseland and Canna cinemas are not eligible for the VPF program because they don’t show the requisite number of new movies. And that’s because studios require exhibitors to sign multi-week contracts to get the best films. Thus a cinema that doesn’t have a second screen to move a fading title and fulfill the contract is penalized.

Eisentraut laments that he probably can’t afford to convert the Canna in Gillespie, a relatively small single-screener that had been closed for a decade before he renovated it in 2007. “It’s a struggling town,” he said. “Without an angel, their only theater could be a Redbox kiosk at the nearest Walmart.”

He’s undecided about the Roseland in Pana, an art-moderne landmark that has almost twice the seating capacity of any theater in St. Louis — in a town with fewer than 6,000 people. But he’s committed to converting the Orpheum in Hillsboro, which has a second auditorium in the former balcony. It draws patrons from as far away as Springfield, Ill., and St. Louis, both of which are an hour away, with amenities such as leather love seats and table service.

Like many small-town exhibitors, Eisentraut is negotiating for digital upgrades through Sonic Equipment Co., a division of the venerable Missouri-based chain B&B Theatres.

Eisentraut, 52, first managed a movie theater at age 15 in his native Iowa. In 2003, his movie-loving wife, Julie, and their four grown children urged him to buy the Orpheum theater, which was built in 1919 by a bootlegger from Panama and run by a regional exhibitor named Norman Paul.

The Eisentrauts now live walking distance from the Orpheum, in a historic Hillsboro home where Abraham Lincoln once stayed, and jointly manage the three theaters. They are bullish on small-town America and continue to scout for Main Street cinemas that might have been converted to community playhouses or antique malls when regional chains such as Kerasotes and the now-defunct Frisina left town. But Jeffrey Eisentraut, who writes a regular column for the trade magazine Box Office, recognizes that a successful operator must evolve with the times.

Patriarch Jeffrey says that his role model is Sid Grauman, the Hollywood showman who placed celebrity footprints in the courtyard of his Chinese Theatre.

“He loved movies, he did crazy stunts, and he died a pauper.”