Regular scanners of the repertory movie listings have likely encountered it: an ad for a free screening of an Ingmar Bergman drama, say, or a little-known silent movie, hosted by, of all places, the New York Public Library. The events draw upon a lesser-known jewel of the library’s holdings: its collection of 16-millimeter films, which is accessible for borrowing by patrons, beloved by its diehard fans, and still going strong.

Not that the collection has been entirely immune to the urban churn of new squashing old: This Monday marks the shuttering of the collection’s former home, the Donnell Library Center (slated for replacement by a hotel, with space allotted for a library branch). But the hardy 16 mm films — which include features, documentaries, experimental projects, and other titles that the library has been collecting since 1953 — were safely taken up this summer by the Library of the Performing Arts at Lincoln Center.

The continued availability of the reels reflects the public library’s resilient commitment to a medium that the digital age has been all too willing to consign to the trash.

Unlike many other libraries around the country that also started collecting films in the ’50s, the New York system has retained its holdings and even plans to expand access through screenings at local branches throughout the city. The dedication goes to the heart of the purpose of the collection as a community resource. Through the years, though, the intended uses have changed.

“The collection was begun out of public demand during the war years, when film was used at the community level to advance the war effort,” the principal librarian at the Library for the Performing Arts Reserve Film and Video Collection, David Callahan, said. Mr. Callahan added that after the war, with the emergence of art and institutional films, the Direct Cinema documentary movement, and the American avant-garde, the collection’s purpose shifted to education and entertainment.

“When I was a kid growing up, my father used to borrow 16 mm prints from our local public library to watch at home,” Mr. Callahan recalled.

Nowadays, few may count a projector as part of their home entertainment system, but the prints still circulate anyway. The library itself screens Hollywood features and less mainstream fare on 16 mm projectors. Mr. Callahan noted that borrower demand is constant for works by cinéma vérité pioneers Jean Rouch and the Maysles brothers, and for avant-garde classics by Stan Brakhage, Ken Jacobs, and Jordan Belson. The collection is also regarded as a major resource for repertory programmers and scholars.

“Part of what makes the collection vibrant is people’s use of it,” a fan of the collection, the artist and filmmaker Jeanne Liotta, said. For more than 15 years, Ms. Liotta has programmed Firefly Cinema, an outdoor film series on the Lower East Side, chiefly using NYPL prints. Besides the serendipity of exploring the collection, she also cherished the chance to display titles “in glorious 16 mm,” a medium she compared to stained glass. “It’s the best-kept secret in New York,” she said.

But the value of the collection also extends outside the city, as a result of the dwindling retention of 16 mm prints by libraries across the country. One Shakespeare scholar recently found at the library the only remaining print of an all-black 1960s production of “Othello.” Even setting aside specific rarities, the ranks of public 16 mm holdings continue to thin, aggravated by the digital-age canard that everything is available on DVD and the Internet. (The critic Dave Kehr has even argued that the glory days of the 16 mm non-theatrical market, plus television syndication, probably kept alive more titles than the current blood-from-a-stone flow of DVD box sets.)

Fortunately, New Yorkers don’t have to choose. The fruits of the library’s 16 mm holdings are plentifully available at library screenings, which are slated to expand as part of a concerted initiative. On September 3, for example, the 96th Street branch will show the 1955 Alec Guinness classic “The Ladykillers”; on the same day, the Bronx Library Center will unspool a more modern confection: “Shrek.” And beginning in October, the Bruno Walter Auditorium at the Library for the Performing Arts will pick up where the Donnell Center left off with free screenings on Tuesdays and Fridays at 2:30 p.m. It will begin with Bob Hope films on Tuesdays and a Derek Jarman series running Fridays.

If that sounds as eclectic and ambitious as some of the repertory houses that charge admission, that’s no accident.

“Folks I’ve spoken to at neighborhood branches say that with the closing of movie theaters in their areas, the demand for a common space for people to come and watch movies together has really gone up,” Mr. Callahan said. “That’s really important, not just because of the decline of repertory theaters, but the closing of movie theaters in general.”

Crucially, the library’s ability to hold screenings stems from the institution’s practice of acquiring prints with performance rights. Patrons can also screen the prints for free; if charging admission, the usual route through distributors or the filmmaker is necessary. The library, which currently holds more than 6,000 titles, also regularly screens films preserved by its staff, in accordance with grants received for the endeavor.

Recently preserved (and screened) titles include the only known print of Susan Sontag’s “Promised Lands,” as well as beautiful New York documentaries about the Fulton Fish Market, pigeon coops, and the World Trade Center. Current preservation projects include the works of the clay-animation filmmaker Eli Noyes, and “Around My Way,” a 1960 film composed of children’s drawings depicting their impressions of the city — once a staple of library film collections, now a rarity.

Digital cameras may have usurped the rough-and-ready role of 16 mm film among younger filmmakers, but there remain decades of riches in the New York Public Library’s 16 mm collection yet to be fully appreciated. Like most libraries and museum collections, it is a quiet sanctuary amid the unending urban churn of new replacing old. But this is one secret that begs to be let out.