Why Dorothy and Toto are a hard act to follow

BECAUSE ... of the world L Frank Baum created. Lyman Frank Baum wrote 14 Oz novels between 1900-1920, creating a vast and detailed universe for young readers to explore. Franco, who read all the Baum books growing up, says he signed up to Raimi's film because it had familiar facets, including the Emerald City, munchkins and that colourfully monoblocked road, while being different in one crucial respect from the classic 1939 film version. "They were respectful of what they should respect and innovative when they should be innovative."

In Raimi's prequel, the central character is not a young Dorothy but Oz, a ducking-and-diving circus magician who arrives in the troubled kingdom and is mistaken for the emperor. There have been other attempts to channel the power of Oz on screen: among them a silent version made in 1925; Return to Oz, a tepidly received sequel released in 1985; and the all-singing-and-dancing flop that was The Wiz, starring Diana Ross as Dorothy and Michael Jackson as the scarecrow.

BECAUSE ... the 1939 version has a place in the pantheon of film greats. Directed by Victor Fleming and starring a 16-year-old Judy Garland, The Wizard of Oz arrived just as a decade of economic misery was about to give way to a world war. If anyone needed to be transported from the black and white of reality to the colourful and magical land of Oz, it was the audiences of 1939. With its messages of hope, daring use of colour, catchy songs and daffy humour, Oz appealed to all ages. Not a box office smash initially, it was television that brought the film to successive generations. Raimi describes his Oz as "a love poem" to the double Oscar-winning 1939 film (best music, and best song for Over the Rainbow). "For me it was the scariest picture ever made, the sweetest picture ever made and the greatest musical ever made."

BECAUSE ... of the characters. Oz the Great and Powerful has a trio of witches: Evanora (Weisz), Glinda the good witch (Williams) and the Wicked Witch of the West (Kunis). In place of the Scarecrow, the Tin Man and the Cowardly Lion, Oz is accompanied on his quest by a flying monkey called Finley (voiced by Zach Braff of Scrubs) and a china doll. Wisely, there has been no attempt to replace that giant among canine film stars, Toto, played in the 1939 film by Terry, a Cairn terrier.

BECAUSE ... of the costumes. For Raimi's film, designers Gary Jones and Michael Kutsche created close to 2000 costumes. Among the most spectacular are those for the witches. "My character would have been nothing without the sequins, the feathers, the lashes, the corset, the boots, the nails," says Weisz. "I've really only played characters who wear jeans and T-shirts and have a scrubbed face. Evanora took a couple of hours to get in place." The care taken extended to the props, too: the gold coins that feature in the film have an image of L Frank Baum on one side and the yellow brick road on the other. As the rights to the 1939 film are owned by a different studio, several costume areas were a no-go, including Dorothy's ruby slippers.

BECAUSE ... Baum's tale pushed the boundaries of cinema. Just as the 1939 picture wowed audiences with its use of Technicolor and black and white, so Raimi is hoping audiences will be impressed by his use of 3D. Shot on a huge soundstage in Michigan, this is the first film the Spider-Man director has made in 3D.

"The land is a very important part of Baum's work, the magical land of Oz, and I wanted to describe it as richly and deeply as possible," he says. "That extra tool of the third dimension was a great thing to invite the audience into that land so that they can feel it and touch it. But would it be right for another picture? I don't know." Raimi is such an admirer of the 1939 picture he hesitated long and hard over Oz. "I was actually very frightened to approach the project because there is so much love for the original Wizard of Oz picture, and people don't want their warm feelings towards this great classic sullied. They don't want someone stepping on their fun, those memories of their childhood."

It is a gamble for Disney too. The budget, according to a report in the New York Times, was $325 million (£215 million). Raimi says it was the script by Mitchell Kapner and David Lindsay-Abaire that ultimately won him over. It was such a sweet and moving story, he says. "The moment I had that feeling I thought, all will be forgiven. If I can bring this feeling to the fans of the Oz books or the movie, only a wicked old witch wouldn't want that picture to be made."

Oz The Great and Powerful opens tomorrow