In the exhibition “The Way Back,” the photographer presents unseen outtakes from his nearly 70-year career as a chronicler of American life.

Breathtakingly fast and painstakingly slow: Before the introduction of the digital camera, a photographer worked in those parallel time frames. The click of the shutter was instantaneous, but then the film had to be developed, the contact sheets or color slides reviewed, and the selections made for printing.

Pressed for time, a working photographer typically made these decisions hurriedly. In old age, there is time for reconsideration. Bruce Davidson, who turns 90 next month, has been reviewing his archive for the last eight years. In “The Way Back,” the title both of an exhibition now at the Howard Greenberg Gallery, in New York, and a more compendious book to be published this fall, he is presenting photos he overlooked, putting them on public view for the first time.

In a 2015 interview, Davidson named for me some photographers he thought had taken the art form to “a new departure point”: Eugène Atget, Henri Cartier-Bresson, Robert Frank, Diane Arbus. He did not include himself. He knows he has followed trails blazed by pioneers. What makes him remarkable is the empathy that won over his subjects and the devoted persistence of his investigations.

A photograph from Davidson’s breakout series, “Brooklyn Gang,” 1959, when he embedded himself with a gang of teenagers in pre-gentrified Park Slope.via Bruce Davidson/Magnum Photos via Howard Greenberg Gallery, New York

Frank, who is probably Davidson’s greatest influence, restlessly sought to portray scenes and people new to him; it is one reason he did not enjoy or succeed at the lucrative task of crafting photo essays for Life magazine. In contrast, Davidson has preferred to mine the same subject for months or years, getting so close to people that you come to feel you know them yourself.

Davidson broke into professional photography at Life. Fascinated by the camera from the time he was 10, he was encouraged by his stepfather, who advised him to apply to the Rochester Institute of Technology. From there, he went to study photography at Yale, where his photographs of the college football team garnered five pages in Life. In his 20s, he had begun his professional career.

In an early series on the circus in 1958, he took intimate photographs of Jimmy Armstrong, a clown with dwarfism. He showed Armstrong playing the trumpet in a shabby bedroom, depositing cash at a bank window, performing in makeup and costume, and eating a sandwich alone in a diner. The book “The Way Back” includes another version of the previously published trumpet picture, taken from a greater distance and a lower angle to reveal Armstrong’s living quarters. It discloses more but delivers a slightly lower impact. It made me think of a jazz singer’s alternate version, in which you can better discern the lyrics but lose a bit of the mood.

In a photo Davidson took in the Bronx in 1963, a young man leads off a woman whose headband accents a bouffant flip.Bruce Davidson/Magnum Photos via Howard Greenberg Gallery, New York

The risk of unlimited empathy is sentimentality, a pitfall that tripped up a youthful Davidson at times in his pictures, including those of Armstrong and another favorite subject, an elderly Parisian widow. His breakthrough came soon enough, in 1959, when he embedded himself with a Brooklyn gang of teenagers who ruled a bit of turf in pre-gentrified Park Slope. Like a sputtering match, the kids saunter, primp and canoodle for Davidson’s camera, before they will ineluctably succumb — as Davidson’s wife, Emily Haas Davidson, established in a 1998 interview with a former gang member — to addiction, despair and suicide.

One classic photograph (which surpasses anything in this collection of outtakes) portrays a beautiful young woman with remarkable eyebrows smoking a cigarette and pushing back her hair, as she looms, knowing and defiant, above three of her friends who are intertwined on a blanket in Prospect Park. (At the gallery, she can be seen, charismatic as ever, in another shot where she has joined them on the blanket.) It is a memorably poignant image that would make a nice pendant to one of the Brooklyn gang pictures in the Greenberg show — a boy standing on a gritty street with cupped hands catching the rain.

Davidson’s “East 100th Street” series, taken between 1966 and 1968, focused on residents of a single block in East Harlem, Manhattan.via Bruce Davidson/Magnum Photos, via Howard Greenberg Gallery, New York

Along with the Brooklyn gang, which is the best represented, there are also alternate takes at the gallery from two other major Davidson projects: his documentation of the civil rights struggle in the South in the ’60s, including those he took while traveling with the Freedom Riders; and a two-year immersion with a large-format camera among the hard-pressed Hispanic and Black residents of East 100th Street in East Harlem. In both, he crossed the racial divide and earned the trust of his subjects.

But the two pictures in this rediscovered trove that stick with me most are from lesser known undertakings. Both feature women with big hair. In a photograph taken in the Bronx in 1963, a young Hispanic man clutches a box of what appear to be candy bars in one hand while he leads off a woman whose white headband accents a bouffant flip. Her stare at the photographer — and therefore at the viewer of the photograph — is what arrests you: direct, tough and savvy beyond her years.

A portrait taken in Yosemite National Park in 1965, part of a series Davidson made of people relaxing in a camp site. via Bruce Davidson/Magnum Photos, via Howard Greenberg Gallery, New York

The other portrait was taken in Yosemite National Park in 1965, part of a series Davidson made of people relaxing at a camp site. A wry rejoinder to the wilderness photographs made there a century before by Carleton Watkins, Davidson’s pictures displayed how Yosemite by this time catered not so much to adventurers but to citified tourists, like a young woman with a startling beehive hairdo who sits placidly at a picnic table laden with her provisions. A big gas-guzzling car is parked beyond her. Sharp but not mocking, the Yosemite picture, like the civil rights and East 100th Street projects, was Davidson’s report on what he found in America. Neither doom-saying nor starry-eyed, he was simply being observant. And honest.

Bruce Davidson: The Way Back

Through Sept. 16, Howard Greenberg Gallery, 41 East 57th St, Manhattan; 212 334-0010, howardgreenberg.com