The September Issue, Edinburgh International Film Festival, Edinburgh

Already the reputed inspiration for the monstrous Meryl Streep character in The Devil Wears Prada, Anna Wintour, the legendary British-born editor-in-chief of American Vogue, now gets a documentary all to herself. Based around the creation of the September 2007 issue of the magazine – weighing nearly 5lbs, it's the single largest magazine ever published – Wintour takes centre stage in what feels like an attempt to rescue her post-Prada reputation. "Is she the high priestess of fashion?" asks director R J Cutler, early on. "I would say Pope," comes the reply from one of her minions.

Cutler, who previously followed Bill Clinton's 1992 presidential election campaign in The War Room, gets what initially seems like unprecedented access. Beginning five months before the issue is published, he follows the creation of the magazine as a serious of stylists, editors, fashion designers and models all come together to work on this special issue ("September is the January of fashion," explains one, in one of the film's many proclamations that could easily have come from the mouth of Sacha Baron Cohen's fashionista Brüno).

Indeed, there are times when both Cohen's comic creation and Ben Stiller's thick-as-a-plank male model Derek Zoolander don't seem too outlandish after all. In the closing-credits sequence, rising designer Thakoon, on hearing that his work has made the September issue, jumps for joy before exclaiming, "When's it coming out?" The industry's obsession with perfection is also plain to see. A photograph of Sienna Miller, who is the issue's cover star, is rejected for her smile being "too teethy", while Cutler's cameraman, who gets included in a photo shoot, is told by Wintour that he needs to "go to the gym".

While the film successfully captures the buzz of putting such a mammoth media project together, people expecting a warts-and-all portrait of Wintour will be disappointed. With her designer shades frequently clamped to her face, she remains just as much of an enigma as ever. The only revealing moments come when she's put on the spot about her family. Her father, former London Evening Standard editor Charles Wintour, retired because he got too angry, he once told her. "I get quite angry," she adds, "so I try and restrain that."

It's a pity, then, that we never see Wintour throw a true hissy fit. While Wintour starts the film by noting "people are frightened of fashion", Cutler never quite shows why they're frightened of her. Perhaps the most telling moment comes from her switched-on daughter Katherine. Of the belief that fashion is a "weird industry" and that there's more to life than clothes, when she announces that she's planning to go to law school, her mother blurts out, "We'll see."

When the camera's not following her into meetings with designers like Oscar de la Renta or Jean Paul Gautier, what Cutler is interested in is the impact of Wintour's taste-making editorial decisions, which primarily affect Vogue creative director Grace Coddington. A former Vogue model, the Welsh-born Coddington gives as good as she gets. When a beautiful 1920s-themed shoot she's conjured up is rejected, at vast expense, she's not afraid to let her frustrations show in front of the camera. Indeed, an awkward silence when she and Wintour are waiting for a lift to arrive speaks volumes.

If it's a shame that Cutler didn't capture more of these moments, the fact he even got his foot in the door of Vogue's plush New York offices is to his credit. While there's no doubt that the final cut met with Wintour's approval before it was ever seen, it doesn't come across entirely as a glorified advert for Vogue. Fast, funny and full of energy, as a study of high-end magazine journalism at its most self-important, The September Issue is hard to beat.

'The September Issue' opens on 11 September