In 1956, a French photographer called Marc Riboud met a writer called Han Suyin at the coronation of the king of Nepal. Riboud, who had joined photography agency Magnum in 1954, had immediately travelled to Asia. He had just spent a year in India when he met Han, half-Belgian and half-Chinese, and now probably best known as the author of autobiographical novel A Many Splendoured Thing. She had been to university with a Chinese woman later to become a close associate of Chinese premier Zhou Enlai, and encouraged Riboud to visit China.
China was then an utterly forbidden land for foreigners. Riboud was curious to see for himself what lay behind its bamboo curtain but believed such a trip was impossible. Several months after his meeting with Han, however, he was told he had a visa and could enter China on January 1, 1957. He flew to Hong Kong, where he bought film; then he travelled to the border and walked across the bridge that separated the British Empire from the People's Republic of China.
'I saw the Chinese flag and how it was trying to be higher than the British flag - what is it called? Yes, the Union Jack. It had to be higher, higher.' Riboud, sitting in the Mandarin Oriental hotel, made a sudden gesture with his hands, reaching into the air. He smiled wryly and shrugged. 'Sorry, I go into the detail. The detail which nobody sees, in the photograph that is most important.'
More than 40 years after he first saw the red flag that New Year's Day, Riboud is recognised as the man who has visually mapped the details of China's fitful journey into the 21st century. After his 1957 trip, he returned in 1965 for five months, and again for two months in 1971; he calculates there were eight shorter trips after that until the last, in 1997. Each time, he took out his camera and charted the erratic graph of progress; as a former engineer, he must have taken intellectual pleasure in briefly pinning down the strange, unpredictable mechanism which has been Sino-evolution. No one can ever say for certain what makes China tick, but the photographs on these pages are a black and white flicker of its turning cogs.
There will be no more such lengthy forays. When we met last week, Riboud was planning a trip to Shenzhen, since cancelled. His days of roving China are over - not just because he will turn 78 next month, but because his observer's passion for the mainland has dwindled. 'I have less interest in going to China when China is looking like us.' Instead, he came to Hong Kong to open an exhibition of his work, Marc Riboud 40 Years Of Photography In China, which will continue at 10 Chancery Lane, Central, until June 14. Many of the signed prints on sale can also be seen in the book Marc Riboud In China (published in New York in 1997 by Harry N. Abrams). I took a copy with me, and while we talked for several hours Riboud glanced through its pages; with much volubility and good humour he recalled the past and another country.
That he should be one of life's watchers seems to have been pre-ordained. He was the fifth of seven children, so silent that within the family he was known as 'the taciturn one' (he has made up for this childhood characteristic). When he was seven, a couple he met when he was out riding his bicycle in the country lanes around Lyons, France, handed him their camera and asked him to take their picture as they kissed; he never saw his first photograph but as an introduction to the art of voyeurism, that vignette has a cinematic quality worthy of director Francois Truffaut.