Hidden necrophilia in Vertigo, glowing milk, an on-set spat with Montgomery Clift … in 1962, Alfred Hitchcock revealed his tricks, and the often shocking meanings behind his films, to fellow director François Truffaut. Now their talks have been turned into the revealing film Hitchcock/Truffaut

There’s a derangingly perverted scene in the 1958 film Vertigo. The femme fatale Judy, played by Kim Novak, appears before Scottie, James Stewart’s retired cop, in a sleazy motel room. She’s dressed as the dead woman with whom he’s obsessed. “I indulged in a form of necrophilia,” the director Alfred Hitchcock told François Truffaut during a week-long series of interviews they did in Hollywood in 1962.

Scottie has insisted that Judy dye her hair blond and wear the outfit he bought. Only then will he be able to have sex with her. But there’s a problem. Scottie can’t consummate his desire because one detail is wrong: Judy is wearing her hair down. The dead woman, Madeleine, wore it up. “This means,” Hitchcock explains to Truffaut, “she’s stripped but won’t take off her knickers.”

Scottie sends her back to the bathroom and sits impatiently on the bed. “He’s waiting for the woman to come out nude ready for him,” Hitchcock adds. “While he was sitting waiting, he was getting an erection.” Then Hitchcock tells Truffaut to turn the tape off so he can tell a story. We will never know what it was, but the safe money says it was really dirty.

Facebook Twitter Pinterest Truffaut seduced Hitchcock into doing 30 hours of interviews, which included chats about Kim Novak in Hitchcock’s 1958 film Vertigo. Photograph: Allstar/Cinetext/Paramount

Kent Jones’s engaging new documentary Hitchcock/Truffaut teems with such moments: the 30-year-old tyro French director asking his hero to explain how he made his films, and the 63-year-old responding in detail, often revealing the lubricious impulses behind such masterpieces as Psycho, The Birds and Marnie. For 50 years, these conversations have existed in book form. Jones has set them free, juxtaposing the audio recordings with relevant scenes from the films.

Hitchcock clearly revels in disclosing some of his secrets. As we watch the superbly sinister scene in the 1941 thriller Suspicion in which Cary Grant slowly, but implacably, ascends a spiral staircase towards Joan Fontaine’s bedroom, we may well wonder why the glass of milk he’s carrying looks so ominous and hyperreal. Because, Hitchcock explains, he lit it from inside with a little lightbulb. Truffaut gasps.

Truffaut had seduced Hitchcock into doing 30 hours of interviews by means of an imploring letter: “Since I have become a director myself, my admiration for you has in no way weakened; on the contrary, it has grown stronger and changed in nature. There are many directors with a love of cinema, but what you possess is a love of celluloid itself.” Hitchcock, flattered, telegrammed back in French from Bel Air: “Dear Mister Truffaut, your letter brought tears to my eyes, and I am very grateful to receive such a tribute from you.”

At the time, Truffaut had made just three films, including his semi-autobiographical debut, Les 400 Coups, while Hitchcock was editing his 48th, his extraordinary and probably self-revealing account of sexual repression, Marnie, starring Tippi Hedren and Sean Connery.

Truffaut’s aim was to liberate Hitchcock from his reputation (one that the Englishman cultivated) as a light entertainer and celebrate him for what he was, a great artist. “It’s wonderful that Truffaut got Hitchcock to talk because directors of his generation didn’t often,” says Jones, head of the New York film festival, and the director who collaborated on Martin Scorsese’s survey of Italian cinema, My Voyage to Italy. “They were dismissive about their art, at least publicly. John Ford would say, ‘I only make westerns.’ Howard Hawks would say, ‘I only make comedies.’ They weren’t inclined to talk seriously about their work, partly because they needed to survive in the studio system.”

Hitchcock and Truffaut were from different cinematic cultures. Hitchcock had made the first of his pictures in the silent era and went on to work in Hollywood. Truffaut was initially a critic for Cahiers du Cinéma. Thanks to critics such as Chabrol, Rohmer, Rivette, Godard and indeed Truffaut (all of whom who would become the iconoclastic hipster directors of the Nouvelle Vague), cinema for the first time became, as director Olivier Assayas puts it in Jones’s film, self-conscious. For the first time, it reflected on itself as art rather than dismissing itself as mere entertainment. The Hitchcock-Truffaut interviews were part of that revolution.

Truffaut and Hitchcock began their interviews on 13 August, Hitchcock’s 63rd birthday. Four years later, the interviews were published. “It has been an incredibly influential book,” says Jones, adding that it was pivotal in the education of film-makers such as Coppola, De Palma, Lucas, Spielberg, Scorsese, Friedkin and Schrader. Today’s generation, it seems, is no less in awe. “When I asked David Fincher if he’d read it, he said, ‘Only, like, 200 times.’”

There are only two moments when Hitchcock clams up. First, as Truffaut suggests, quite sensibly, that the lack of realism and plausibility in Hitchcock’s movies (think of the scene in North by Northwest when Cary Grant emerges unscathed from a fireball caused by the crop-dusting plane that’s been pursuing him crashing into a fuel truck) is because his pictures yield to a deeper logic, the logic of dreams. “Hitchcock just doesn’t want to go there,” says Jones. “He’s not comfortable with that level of disclosure.”

Yet, as Fincher, one of 10 present-day directors whom Jones interviews for the film, argues, one of the exciting things about Hitchcock is that his fears and fetishes, his nocturnal terrors and his sexual daydreams, are all over his work. Indeed, for Fincher, one of the lessons of Hitchcock’s cinema is that any film-maker who thinks they can stop their psychopathologies leaking on to the screen is, as he puts it, “nuts”. Jones says: “I think David’s right. Hitchcock does what he wants, and indeed, if you look at those film-makers who try to do what others want, or what they think the audience want, they come unstuck.”

The other moment is when Truffaut, again quite sensibly, argues that Hitchcock’s trademark omniscient shots (the terrifying airborne shot of the town on fire in The Birds; the camera descending from Olympian heights to find the compromising key in Ingrid Bergman’s hand in Notorious) could have been made only by someone raised, as Hitchcock was, a Catholic. Hitchcock asks Truffaut to turn off the tape so he can go off record. “Again, we don’t know what he said, but he clearly didn’t want to reveal his motivations,” says Jones. Instead, in Jones’s film it’s left to another Catholic director, Scorsese, to clinch the point: the God-like perspective of Hitchcock’s aerial shots induce terror.

“In the book of the interviews,” says Jones, “Hitchcock came over as stilted and formal, which you can hear he isn’t.” Quite so: Hitchcock is often droll and cantankerous. “Actors are cattle,” he tells Truffaut, underlining his reputation for giving them no scope but to fulfil his artistic vision. “He can’t mean that,” says Jones. “Yes, he started in cinema during the silent era, well before the post-war era after which, as Scorsese says, the power shifted to the actor. But he wasn’t contemptuous – he had immensely fruitful relationships with actors.”

True, but Hitchcock was always boss. The film recalls his on-set spat during I Confess with Montgomery Clift over a split-second moment in which the actor was required to look up at a building as he crossed the street. The method actor who had trained with Lee Strasberg said he needed to consider whether his character, a guilt-ridden Roman Catholic priest, would look up at that moment. Hitchcock didn’t care what Clift thought: he needed him to look up at that precise moment or everything leading up to and from that glance would not make sense. Truffaut, when Hitchcock explains this to him, agrees: if Clift refused, he would have ruined the story arc. Happily, Clift ultimately glanced upwards and the scene makes sense.

Facebook Twitter Pinterest Jeanne Moreau in Truffaut’s 1962 film Jules et Jim. Photograph: Ronald Grant Archive

Truffaut, for all that he was profoundly influenced by this father figure, gave actors more leeway. He tells Hitchcock about a scene in Jules et Jim that his three actors improvised. Hitchcock is incredulous: he could never allow that.

Later, Jones reveals, Hitchcock worried that he was too rigid in his commitment to narrative rigour. Perhaps he should have given his actors more freedom. In one telegram to Truffaut, he says how difficult it would have been for Mondrian to paint like Cézanne: by which he means how difficult it would have been for Hitchcock to direct like Truffaut, or indeed like others in the Nouvelle Vague, still less like the great American directors of the 1970s who allowed their actors a great deal of freedom.

It’s a point taken up by Fincher, who wonders how Hitchcock would have got on directing such actors as De Niro, Pacino and Hoffman. “Sadly, we’ll never know,” says Jones. “But he did have conflicts with actors who were less willing to respect his authority, not just with Clift on I Confess and Paul Newman on Torn Curtain.”

In any case, he did try to loosen up, to mutate, as it were, from Mondrian to Cézanne. “There is some 16mm test film provisionally called Kaleidoscope/Frenzy, in which he tried to be freer and give some young kids in New York the chance to express themselves as actors.” But that film was never made. Instead, in 1972 he made Frenzy, his penultimate – and psychosexually deranged – film, in which Barry Foster strangles his victims with a necktie, grunting: “Lovely! Lovely!”

Almost two decades after Truffaut and Hitchcock recorded their interviews, the Frenchman was still lecturing the world on his hero’s merits. “In America,” Truffaut told the American Film Institute in 1979 during a homage, “you call him Hitch. In France, we call him Monsieur Hitchcock. In America, you respect him because he shoots scenes of love as if they were scenes of murder. We respect him because he shoots scenes of murder like scenes of love.”

The following year, Hitchcock died. All too soon Truffaut followed him in 1984, aged only 52, and at the height of his powers.

• Hitchcock/Truffaut premieres at Cannes on 19 May.

• More on Hitchock: Holocaust documentary whose horrors remained unseen reaches cinemas – after 70 years.