A crude measure of their collective achievement can be seen in the number of exhibitions notched up between them. 1999 has already seen last year's Citibank prizewinner Andreas Gursky have a welcome if flawed one-man show at the Serpentine. The Bechers have just vacated Sheffield's Site Gallery. Both Struth and Ruff have recently had major retrospectives in Paris, and Jorg Sasse, another young Becher student (seen in the ICA's 1998 show New Sightings), is presently enjoying a second solo outing at New York's Lehmann Maupin Gallery. At any given time pieces by all of them can be found in group shows around the world, and later this month the Architectural Association is publishing a book to accompany an exhibition - Reconstructing Space: Architecture in Recent German Photography - that includes pictures by Becher and his wife, and work by 10 of his former students.
According to Becher, his was a hands-off approach, limited to telling his charges only what they should not do. He believes that those who went on to make names for themselves would have done so with or without him, as they arrived at the Akademie with strong ideas, strong personalities and a willingness to work. His modesty is sincere if not convincing, for it is a truism that the most promising pupils seek out the best teachers, understanding beforehand what they want to learn from their chosen masters. Besides, in the world of art photography the Bechers' reach has long stretched beyond the confines of Dusseldorf's campus.
In the early Fifties, when the Bechers were themselves students at the Kunstakademie, they found themselves at odds with the dominant abstract expressionism. Even though a tradition of strictly objective photography had been established back in the Twenties by August Sander, Karl Blossfeldt and Albert Renger-Patzsch, the post-war climate in Germany favoured a solipsistic, subjective approach to art in general and to art photography in particular - perhaps a subconscious way of deferring any painful scrutiny of the country's recent past.
By contrast, the Bechers' approach to their subject matter was, right from the outset, unblinking and direct. Photographing those structures that caught their attention head on and under neutral, overcast skies so as to avoid any confusing shadows, their intention was to establish utterly legible typological surveys of the blast-furnaces, mineheads, water towers and other constructions that are part and parcel of industrial landscapes. Their powerful body of work has been linked to several movements, including minimalism and conceptual art.
It is the photographs taken by his one-time apprentices that bear the clearest stamp of the couple's influence. In Hofer's pregnant, institutional interiors, in Struth's deserted streets and in Ruff's unflinching portraits, there is a methodological integrity that prohibits any subjective interference with what is being documented. It is the same integrity that is the overriding hallmark of the Bechers' output.
In 1975, the artist Lewis Baltz suggested that the ideal photographic document would be one without author or art. Although the work of every one of these photographers is eminently recognisable, it is marked by a diminution of authorial presence that allows those things being photographed to speak for themselves. Yet paradoxically, because of the stillness of what is depicted, the subjects of their pictures also remain imperturbably mute and beyond description. The power of these austere, unromantic meditations on our world derives from their measured simplicity. Photography is fundamentally a recording device. In the hands of the Bechers and their students, whose various approaches are underpinned by a conceptual rigour that refuses both spectacle and pictorialism, it produces incontrovertible results that remind us of the ability of this medium to focus our attention on the facts.
Andreas Gursky's epic pictures of man projected into a matrix of his own making are perhaps the most incontrovertible of the lot. The images generated by his God's-eye view of urban spaces, stock-exchange floors and hotel atria, are startling to behold. But since 1992 this one-time Becher student has begun to manipulate his photographs digitally. "I subjugate the real situation to my artistic conception of the picture," he recently told an interviewer. Where once unadulterated reality held sway, we are now shown a version of it as conceived by Gursky. Such a didactic attitude is a long way from the subtler, Calvinist sensibilities of his mentors, who would never countenance any such imposition of an idea on to the object being photographed.
However, in this respect Gursky may be unique among the Becher students. Even the forthcoming Sasse's striking, painterly creations, which at first glance would appear to be little more than expressions of subjective conceit, are in fact no such thing at all. For Sasse's quiet interest is in the forgotten corners and overlooked elements of other people's snapshots. These he digitally enhances and blows up to a size that makes us take note of an incidental zone that normally inscribes itself only in the margins of our vision.
Yet if Gursky has on occasion chosen to represent reality differently from the Bechers, he still remains in their camp. Three of Bernhard's students have made art a direct subject of their work. But while Hofer and Struth, with their pictures of crowded museums, remind us of its social function, it is Gursky, with his unpeopled photographs of paintings, who enters more specifically into a dialogue with its history. It is significant that to date he has only twice photographed works of art, the first a trio of Turners as they hang in the Tate Gallery, and the second, the same Jackson Pollock - One, No. 31 - that Struth photographed four years before him at MoMA in New York. These paintings exemplify a current that is the polar opposite to the straight photography practised by the Bechers and their inheritors. For Turner gave birth to a romantic and subjective vision that was to achieve its apotheosis nearly 150 years later in Pollock's abstract expressionist canvases. Another half-century on, Gursky has cast the dispassionate eye of the photographer in their direction. To borrow Marshall McLuhan's terminology, he has, by bringing these "hot" eruptions of subjectivity into the photographic frame, "cooled" them down. And in so doing he has continued the objective analysis of the world to which the Bechers have consecrated their lives.
`Reconstructing Space: Architecture in Recent German Photography' is at the Architectural Association, 36 Bedford Square, London W1, from 20 April to 21 May, Mon-Fri 10am-7pm, Sat 10am-3pm. Admission free