Tacita Dean, Tate Modern, Turbine Hall

A moving tribute to the beauty of a dying art

For her installation in the Tate Modern's Turbine Hall, the 12th Unilever Commission, the artist Tacita Dean has revealed a film which is a paean to a dying, or at least endangered, medium: film itself.

There are now only a handful of film labs left in the world that can process analogue film, due to the onslaught of a far cheaper digital format. In recent years, Dean has become well-known for her intimate 16mm film portraits of artists in their old age: Merce Cunningham, Mario Merz, and, most recently, Cy Twombly, who died just after Dean's portrait of him was shown for the first time at Dulwich Picture Gallery.

Here is a portrait of film itself; not only does she reveal the holes at the side of the reels, this work is filmed in portrait format: a huge projection in CinemaScope format (think of those panoramic views from Westerns) turned on to its side.

Dean's film is a tremendously moving exhortation to the medium and to the space of the Turbine Hall – and has been made totally within the camera.

Through blocking out spaces of film and running them back through the camera, Dean can make snails and waterfalls appear in the windows of the old power station. She can bring back Olafur Eliasson's sun for a moment; she can make a small rock in her studio into a huge mountain, recalling the Paramount Pictures logo.

Tate's publication accompanying the show features contributions from everyone from Jean-Luc Godard to Neil Young, who write about the importance of analogue in the digital age. In Dean's film, one senses the last chance gasps of creativity, the glorious, hopeful, cinematic swan dive, as the artist experiments with film – running it through the camera 10 times, masking out sections, cutting and pasting like a moving collage – for what could be the last time.

She pushes and experiments with the constraints that have defined a glorious cinematic history – look what can still be done here. The space is lit by blocks of colour like cathedral windows. The Tate escalators ascend like film reels in a projector. A child's eye peers through a circular hole in the film into the dark. A public clock ticks past a minute. We're not done yet, there's so much more that we can still do together.