"It is with great regret and profound sadness that I have to announce the passing of Martine Franck," writes photographer Alex Majoli, Magnum Photos' president. "Martine was not only an incredibly talented photographer, she was also a dear friend and colleague to us, and an inspiration to many. Magnum has lost a point of reference, a lighthouse, and one of our most influential and beloved members with her death. Her wisdom, wit and intelligence will be missed immensely by all of us."

Martine Franck, born in Belgium, was Henri Cartier-Bresson's second wife and president of the Henri Cartier-Bresson Foundation, established to promote the photojournalist's work. But she was also a photographer in her own right, beginning her career as the assistant of Eliot Elisofon and Gjon Mili at Life magazine, before joining the Vu agency in the 1960s.

Speaking to The Wall Street Journal last year, she said she started her photographic career as a shy young woman. "I never really dared to go up to people and talk to them. I started by taking wedding photographs. Then, when I went to parties, I would take my camera with me, just to give myself a sense of composure, or a necessity to be there."

In 1964, Ariane Mnouchkine introduced her to the Théâtre du Soleil, and Franck quickly became the theatre's official photographer until her death. In 1972, the photographer co-found the Viva agency, while continuing her career as a photographer. "Franck took many portraits of artists and writers, including a noteworthy series of women for Vogue," reads her biography on the Magnum Photos website. "She undertook more far-reaching work for the French Ministry of Women's Rights in 1983. That same year she became a full member of Magnum Photos," just three years after joining the agency as a nominee.

Franck travelled extensively in Asia, photographing Buddhist Tibetan children in India and Nepal. "With the help of Marilyn Silverstone, a former member of Magnum Photos who became a Buddhist nun, she encountered the Tulkus, the young lamas who are thought to be the reincarnations of ancient great spiritual masters," says Magnum Photos.

More recently, Franck participated in the Georgian Spring book project with other Magnum photographers. She published her last book in September 2011, bringing together 63 portraits of artists in their studios, shot over five decades from 1963 to 2010. The book, Venus d'ailleurs, was published by Actes Sud in France.

Franck married Cartier-Bresson in 1970. A year before the "Decisive Moment" photographer's death, Franck, with her daughter, launched the Henri Cartier-Bresson Foundation to promote his work and photojournalism. In an interview with The New York Times, she said of Cartier-Bresson: "Henri taught me to say ‘no.' He taught me to be selective, never to show photographs one did not want to see published. I believe he learned this himself from Alexey Brodovitch at Harper's Bazaar."

"We all knew that Martine was really ill," former Life magazine's picture editor John G. Morris tells BJP. "I had last seen her several months ago, and she herself had admitted that she wasn't well. I've known her almost as long as Henri [Cartier-Bresson] did. I met her through him, of course, shortly after they got together and I knew a little about her previous record as a photographer and I was not surprised when she was taken into Magnum. Quite frankly, my first impression at the time was that she got there only because of Henri, but I think, on the contrary, that she was very reluctant to take advantage of that fact. She wanted to prove that she was worth it."

Morris adds: "She was a very fine photographer. She was just a wonderfully gracious person. She was very humble and very friendly. I would often visit them at their homes in Paris and in Lubéron, and she was always a gracious hostess. I want to pay tribute to her. I think she deserves the recognition that she is now getting."

On Twitter, Magnum photographer John Vink reacted to Franck's death: "Most generous Magnum member gone. Sad. Very sad..."

Speaking to BJP, Michael Pritchard, the director general of the Royal Photographic Society, says: "Martine Franck's work was firmly rooted in the tradition of French humanist documentary photography. She was able to work with her subjects to bring out their emotions and to record their expressions on to film, helping the viewer understand what she had seen in person. Her images were always empathetic with her subject."

He adds: "Although Martine lived partly in the shadow of her husband Henri Cartier-Bresson her own work was distinctive and she was instrumental in preserving Cartier-Bresson's wider legacy and values through the Henri Cartier-Bresson Foundation."

Franck died after a long illness. She is survived by her daughter, Mélanie.

To view some of Martine Franck's work, visit the Magnum Photos website.