Most 'The Making of...' documentaries are barely concealed extensions of the publicity machine, a glorified advertisement that purports to demystify the industrial production of cinema, to bring the audiences closer to actors and directors who are presumed to be engaged as real people creating a fiction, rather than a fiction. When really, the carefully stage-managed featurette reveals just as much as the filmmakers want, tantalising the curious punter without ever enlightening, and developing an extra facet of a star persona, rather than normalising it.

As you might expect, a 'Making of' an Ingmar Bergman film is a little different. Recording the shoot of his swansong and crowning masterpiece, 'Fanny and Alexander', 'Dokument' is essential viewing for Bergmanophiles. Framed by explanatory, often flippant intertitles, the film follows, in detail, Bergman at work, painstakingly, methodically, often tediously shaping each scene, the precise movements of camera and actors, the details of the composition, the timing and delivery of dialogue. There is no frivolous chumminess here, no meet-the-backroom-boys boffinry.

Bergman disclaims at the start any pretensions for this documentary, suggesting that it can never capture the inner journey that is the act of creation: this is of course true, but 'Dokument' is more than the entertaining peek backstage Bergman affects to offer us. With 'Dokument', Bergman performs two very serious functions. Firstly, and perhaps most importantly, he educates the viewer. It many seem dull to watch take after take of each scene, with little of the 'hilarious' bloopers TV programmes and Hollywood end credits delight in (although there's some wonderful business with an intransigent cat). There may not seem to be any real difference between takes, or any reason why we should be shown rehearsals for takes followed by takes.

What this repetition does, though, is accustom the viewer to nuance, to the aesthetic reason for the most functional set-up, or why a character is in this particular position, why this shot is in close up, while the next is an elaborate long take. it alerts us to the use of colour, light, framing; it makes us aware of the details of the decor. The documentary may not show the creative inner journey, but when we see the process from rehearsal to take to final act, we do glimpse something of Bergman's art, something that is clearly going on in his head while the shoot takes place, but remains, until then, unspoken. Trust me, if you watch this documentary just before the film itself, as I did, your mind becomes more receptive, and the work's rich magic becomes even more clearly apparent.

Secondly, and relatedly, 'Dokument' is in a sense a Bergman film. Despite its light, seemingly loose form and tone (Bergman, far from being the anguished dictator of legend, is amiable and constantly braying with childlike laughter), the creative journey I spoke of becomes in a sense a spiritual journey. Like 'Fanny and Alexander' itself, a recreation of Bergman's childhood, the documentary is framed around dinners - in between comes a revelation of the artist, in this case at the end, rather than beginning, of his career.

There is a truly painful sequence here, among the most emotionally powerful in Bergman's work, where Bergman rehearses a cameo with his long-time collaborator Gunnar Bjornstrand, doing a piece as the clown Feste in Shakespeare's 'Twelfth Night'. If the intertitles didn't suggest that Bjornstrand approved the scenes being shown, you would think they were exploitative and humiliating. Bergman may be near the end of his career here, but he is still intellectually and physically formidable, handling the demands of a big-budget, three hours plus costume drama with a large cast and difficult narrative strands with ease and grace.

Bjornstrand, on the other hand, seems nearly senile, tired, forgetful, plainly not up to the job, shown in his scene's non-appearance in the movie. The sight of Bergman trying to keep his friend's spirits up, encourage and compliment a giant of acting like he's a baby, for around 20 minutes, is something you'll never see in 'The Making of Pearl Harbour'. It says so much about Bergman's art and his themes, and how even at his most artificial, he was clearly, obstinately true to life. It's uncanny.