The Imax format has been going for 30 years, but until recently it was a specialised - and rare - experience. The BFI cinema, in its Bryan Avery-designed glass drum, however, marks a turning point. Literally, as it happens, since it sprouts from the undercroft of the South Bank's subway system, right in the middle of the huge elevated roundabout on the southern end of Waterloo Bridge. This is the first big new cultural building on the South Bank since, well, the BFI's Museum of the Moving Image, also by Avery, in 1988.

However, Britain's - and Europe's - first Imax was built in 1983 in Bradford, at the then-new National Museum of Photography, Film and Television (NMP). The NMP has just had a £16m revamp, updating its pioneering cinema for the latest 3-D effects, and has quietly reopened for a test run before an official launch later this month.

There are now more of these new picture palaces than there are films to show in them: 130 Imax films are in distribution, and another 80 are being made. In contrast, there are 180 Imax cinemas around the world, and another 75 are being built. Soon there will be seven in the UK, including two cut-price versions in commercial multiplexes in Manchester and Greenwich. But Imax films remain in repertory pretty much for ever. Simultaneously, big corporations such as Disney and Sony are getting involved (Disney is making Fantasia 2000 for Imax). Even cerebral film-makers such as Peter Greenaway are now said to be expressing an interest in the medium, while an art-house animation of Hemingway's The Old Man and the Sea, by the Russian Alexander Petrov, premieres in the new Imax in June.

Imax films tend to be shorter than most movies - an hour or less, usually, though a few run to 90 minutes. The BFI expects three different audiences throughout the day: schools in the morning, tourists in the afternoon and locals in the evening. It conservatively reckons it should fill half a million seats a year at the Waterloo megadrome. Its equivalent in Berlin is on target for three times that number in its first year.

The format has so far lent itself mainly to National Geographic-style wonders-of-the-world treatment. Outer space. Beneath the oceans. Volcanoes. Ants at work. Nothing much involving human characters or storylines, unless you count a Rolling Stones live concert. Just great for the visitor centre at Cape Canaveral. A few years back, you would have been excused for thinking that this Canadian invention was the Cinerama of our time - an interesting backwater, well away from the commercial mainstream. Not, it seems, any more.