Jane Bown's portrait photographs are well known. Week on week they have been appearing in The Observer, where her first portrait, of the philosopher Bertrand Russell, was published in 1949. That portrait, along with 44 others by Bown, is now in the National Portrait Gallery, but Bown is a far cry from being England's Annie Leibovitz. She never stage-manages her subjects, brings neither props nor lights nor assistants to an assignment, just one of her 40-year-old Olympus OM1 cameras, with a 50mm F2.5 lens, possibly in her shopping bag. She waits while her subject is being interviewed, observing all the time, then quickly snaps three rolls of black and white film. The subject is taken momentarily unawares, the session over before there has been time to assume a public mask. When Bown was at Buckingham Palace to collect her CBE in 1995 she demurred politely when the Queen called her an artist. 'I am not an artist,' she said. 'I'm just a hack.' The understatement was characteristic, but there was a time when she might not have uttered it.
In 1946 21-year-old Bown, newly demobbed from the Wrens, managed to wangle a place in the photography class conducted by Ifor Thomas at the Guildford School of Art. (The Guildford School of Art, which has now been absorbed in the West Surrey Colleges of Art, was both pioneering and prestigious; its most famous alumnus is Dame Elizabeth Frink.) By the beginning of her second term at Guildford, when Bown borrowed £50 to invest in a second-hand Rolleiflex, she had committed herself to serious photography. The Rollei (which is still the camera of choice for David Bailey) was then the only camera for art and magazine photography. Ifor Thomas soon realised Bown 'had an eye' and instilled in her the solid compositional values that can be seen in the best of her early work, whether she was photographing people on the beach, a ball of yarn on stony ground, hop poles against the sky, or a sleek young shark dying on the shingle. The square picture had to be composed first of all by the eye and then framed (the image appears back to front in the viewfinder on top of the Rolleiflex), the exposure set - not by use of a light meter but by judging the intensity of the light on the back of her hand, and the picture shot, once. In a self-portrait with the Olympus she used later, Bown shows her eyes looking over the camera, as if identifying the shot before she looks through the viewfinder - a last reminder of these early days of looking, framing, finding the light, positioning herself and then - all or nothing. The pictures she took in the Rolleiflex years embody the best of the formalist aesthetic of the Fifties and Sixties, the kind of orchestration of line and mass celebrated by the much-lamented Adrian Stokes in his seminal Smooth and Rough, published in 1951.
Though Bown claims not to have been aware of the work of Henri Cartier-Bresson until later in her career, her sensibility seems to have most in common with his. Cartier-Bresson too refused to allow his photography to be called art. He and Bown both describe themselves as 'prowling' in search of pictures. The pictures Cartier-Bresson found with his Leica are wonderful because of his artist's eye choosing the frame, the depth of focus and the distance from the subject, often in a split second - what he called the 'decisive moment'. Cartier-Bresson minimised the artistry of his photographic work because of his deep faith that the photographer's highest duty was to actuality. The objective was, in Cartier-Bresson's own words, 'the simultaneous recognition in a fraction of a second of the significance of an event as well as the precise organisation of forms which gives the event its proper expression'. Bown is saying much the same thing more simply when she says: 'Some photographers take pictures; I find them.'
At first child photography was Bown's bread and butter; when she escaped from the studio and rambled about the country she was after something different, something special. In 1952 when she set off with her camera, whether to Eton, Crystal Palace or Cowes, she was on the same quest as Cartier-Bresson. At Eton she found an Old Boy leaning on his cane, trilby tipped to match the slant of his dropped shoulder, left foot shot forward to counterbalance the angle of the cane. He looks with pursed lips and narrowed eyes at the young woman with the camera, deciding perhaps whether to tell her to 'bugger orf'. He probably thinks he is the subject of the shot, but he shares the frame with a female companion who sits almost at ground level behind him, hunched and hidden by layers of organdie, defending her legs with a big white handbag. The picture crackles with tension which Bown neither explains nor resolves.
In 1957, long before she began regularly to shoot portraits, Bown snapped (her own word) Cartier-Bresson - who was so averse to being photographed that when he was collecting an honorary degree at Oxford he shielded his face with a sheet of paper - squinting into the viewfinder of his Leica, with more than half his face obscured. Photographs of Jane Bown are as scarce as photographs of Cartier-Bresson. The most productive years for what is now called her photo-journalism were the Fifties and Sixties, the years spent raising her three children. Bown was moved by children as subjects, whether they were hanging round the hop-pickers' encampments, or struggling with sums on the school blackboard, but unlike many other women photographers, though she filled family albums to commemorate the usual family events, she almost never used her own children as subjects in her serious work.
These days Bown is more likely to remind people of Robert Frank, Cartier-Bresson having been ranked with the immortals. Cartier-Bresson collected 10 international awards for photography, Bown has none. Nevertheless if we are to assess the best of her photo-journalism it is to Cartier-Bresson that we must turn to find her soulmate. Frank looks on America with an outsider's eye; the faces he photographs in the street are the hard-edged faces of strangers. The images that Cartier-Bresson found on the streets of Berlin, Brussels, Warsaw, Prague, Budapest, Madrid, Beijing, Delhi or Paris are very different. Though we cannot always explain them, we feel we understand them; nothing we see of them, no matter how odd, is threatening. In 2003 Bown said that when she photographs people she is in that instant in love with them. What is evident from her earlier work is something rather different. Whether her subjects are schoolboys, soldiers, haymakers or ponies or even Brussels sprouts under snow, she is momentarily fascinated by them, in awe of them, even. Dingy, dirty and bedraggled though they may be, they are all special. Strings of onions are as precious as the crown jewels; the familiar is revealed as extraordinary, irreplaceable.
In all the images that Bown found in the streets and the countryside, we are struck by the reticence of the camera. Even as she carefully marshals all the elements in her picture, Bown never becomes an element in it. Sometimes one person in a group will be aware of her presence; there is no acknowledgment of communication or recognition. Usually her subjects are not even looking in her direction: she has photographed some of the most expressive behinds in photography. In the hands of Diane Arbus the Rolleiflex oppressed and frightened her subjects even though they couldn't see her sighting them through it. Arbus's gaze curdles the air her subjects breathe, emptying them of their humanity, whereas Bown's treatment of framing and distance allows the space between her and her subjects to seem theirs rather than hers. Though she was as diminutive in stature as Bown, Arbus intruded on her subjects and made a pictorial point of the intrusion. Infants on the end of her lens howl in terror; young couples look up, dwarfed and distorted. Bown believes that a photographer should be neither seen nor heard. Rather than orchestrate her moment, she waited for it.
Both Cartier-Bresson and Bown are supremely uninterested in photographic technology. Having learnt how to make satisfactory images with one camera they each remained with that camera, accepting its limitations as imposing a necessary discipline upon their image-making, as well as allowing them to concentrate on the realisation of the subject. Colour would have destroyed one important element of their work - the dramatisation of the subject by the use of light, in both cases available light. It goes without saying that Bown never uses flash. What this means in effect is that she has no truck with the generation of glamour images, and hence her portraits seem truer than those of other photographers. The Sixties saw the rise of celebrity culture, and the gradual waning of Bown's passion for art photography. The earlier Bown's attitude to celebrity had been like Cartier-Bresson's. Rather than photograph the celebrity, she photographed the public reacting to celebrity. She was happier chronicling decisive moments in the lives of ordinary people than making headshots of pop stars, but there was no longer a market for images of Grimsby dockers cycling to work or nannies at the Serpentine or families at the seaside.
When Jane Bown laid down her Rolleiflex and swapped it for a 35mm camera in 1963 she was capitulating to a massive shift in taste and cultural focus. She has said several times since that it was The Observer that made her into a portrait photographer, and there can be no questioning her success in that genre. Occasionally she took the Rolleiflex on assignment, giving us something as remarkable as her picture of the Torrey Canyon disaster of March 1967. It was a remarkable partnership, and I for one am sorry that it had to end.
· Gallery: Unknown Bown, 1947 to 1967
· Unknown Bown 1947-1967 runs 28 Sept to 25 Jan at the Newsroom, 60 Farringdon Road, London EC1R 3GA (020 7886 9898; www.theguardian.com/newsroom). Admission is free. The exhibition is accompanied by a 128-page book. To order a copy for £16 with free UK p&p, go to www.guardianbooks.co.uk or call 0870 836 0749
