The documentary lineup at the New York Film Festival showcases largely hidden worlds of the city and nearby environs.

When Tania Cypriano began filming Dr. Jess Ting at Manhattan’s Mount Sinai Hospital in 2017, he was one of only 40 surgeons in the United States who performed gender-confirming surgery.

“A lot of films about the trans experience have been made, but I wanted to make something new, that would speak to a larger audience,” says Cypriano, whose documentary is entitled “Born to Be.” “Learning what it is to be transgender, what is at stake and what the future of [these surgeries] looks like through Dr. Ting’s eyes was key.”

Ting and a handful of his patients allowed the director to film their surgeries. “We pitched the president of Mount Sinai, David Reich,” Cypriano says. “He looked at the documentary as an opportunity to show the public what Dr. Ting and his team were doing.”

For her four-hour PBS docu series “College Behind Bars,” director Lynn Novick and producer Sarah Botstein gained access to several maximum- and medium-security prisons in New York state. There she documented imprisoned men and women struggling to earn degrees in the Bard Prison Initiative (BPI), a rigorous prison education program.

“I felt that it was very important for the viewers to understand visually and psychically, that all of this incredible academic work and growth was happening within this larger context,” says Novick. “Over time, we built enough trust to get permission to film in the prison’s yard, armory, mess hall and even in people’s cells.”

Shot over four years, the series follows current BPI students as well as alumni. Over the past 20 years, more than 500 BPI alumni have been released, and less than 4% have gone back to prison. The program currently enrolls 300 men and women in six prisons.

D.W. Young’s “The Booksellers,” by contrast, reveals a much smaller world: a community of rare book dealers and collectors, crammed in New York city apartments and historic buildings, helping to keep the printed word alive.

“The value of the work that these dealers and the collectors do is not widely recognized,” Young says. “Their preservation and interpretation of the material that they handle plays a crucial step in understanding history and academic study.”

A fourth doc, Manny Kirchheimer’s impressionistic “Free Time,” meanwhile, shows an otherworldly Manhattan circa 1958 to 1960. The 88-year-old director restored 16mm black and white footage he and Walter Hess shot during that period.

“The film has a lot of children playing outdoors on the streets of Manhattan,” the director says. “I don’t think you see that anymore. I think audiences will be surprised by that.”