Now that the Tim Burton-directed version of Stephen Sondheim's " Sweeney Todd" has finally opened, several big questions have been settled. Can Johnny Depp sing? Yes. How much blood gets spilled? Lots. Is Helena Bonham Carter likely to land the title role in a revival of "Mame"? Not unless Burton directs.

One question remains unanswered: What is it about Stephen Sondheim and Hollywood? Sondheim has been the pre-eminent figure in American musical theater for nearly 40 years. "Company," "Follies," "Sunday in the Park With George," "Into the Woods": Sondheim wrote the music and lyrics for all of these works, each of which has helped extend and redefine the musical. None has been adapted to the screen.

The strangest thing about Sondheim's musicals proving so difficult to adapt is that Sondheim himself has a long and rather intriguing history with Hollywood. A passionate movie fan growing up, he has called the movies his "basic language" and was guest director at that cognoscenti mecca, the Telluride Film Festival, in 2003. Sondheim's fandom can be seen at work in "Follies," whose original production owed at least part of its impact to casting Hollywood's Alexis Smith and Yvonne De Carlo in leading roles. Two of his musicals, "A Little Night Music" and "Passion," are based on movies: Ingmar Bergman's "Smiles of a Summer Night" and Ettore Scola's "Passione d'Amore."

Sondheim has won an Oscar, for best song, "Sooner or Later (I Always Get My Man)," performed by Madonna in "Dick Tracy." He also composed the scores for Alain Resnais' "Stavisky" and Warren Beatty's "Reds." But his movie past isn't limited to music. Sondheim was clapper boy on "Beat the Devil," John Huston's 1953 spoof of the caper movie. Twenty years later he and Anthony Perkins collaborated on the screenplay for a mystery, "The Last of Sheila." He is nothing if not a man of many talents.

The ability of those talents to translate from Broadway to Hollywood is another matter. Prior to "Sweeney Todd: The Demon Barber of Fleet Street" (to give the movie version its full title), just four Sondheim musicals had been brought to the screen: "West Side Story," "Gypsy," "A Funny Thing Happened on the Way to the Forum," and "A Little Night Music." And the first two don't altogether count, since Sondheim wrote just the lyrics.

All four are vexing to varying degrees. None of the principals in either "West Side Story" or "Gypsy" was a singer. In fact, it's hard to think of a less musical trio than Rosalind Russell, Natalie Wood, and Karl Malden in "Gypsy."

Two of the leads in "Forum" could certainly sing, Zero Mostel and Michael Crawford (later the original "Phantom" - Andrew Lloyd Webber, who might artistically be seen as the anti-Sondheim, has had his own movie difficulties). But most of the songs were cut by the director, Richard Lester. Almost as bad was Lester's strenuous opening up of the musical (dancing atop Roman aqueducts, singing in chariots) and hyperactive editing.

It takes just seven words to summarize the fiasco that was the movie version of "A Little Night Music": Elizabeth Taylor sings "Send in the Clowns." You can see for yourself on YouTube, though the version is slightly out of sync (which in a weird way might enhance the experience): search for Elizabeth Taylor and "Send in the Clowns."

"Night Music" was the last Sondheim adaptation until "Sweeney Todd," nearly 30 years later. The obvious explanation for the delay is that Sondheim's subject matter tends to be so unusual - the opening up of Japan to the West ("Pacific Overtures"), presidential assassins ("Assassins"), not to mention a certain sanguinary barber in Victorian England. Furthermore, the musical as a film genre has been on life support even longer than the Western has. It's not as if Hollywood has been panting for the rights to Tony-winning musicals. "Dreamgirls," a far easier sell, took almost as long to make it to the screen as "Sweeney Todd."

Yet the past year has seen something of a mini boom in musicals: besides "Dreamgirls," "Once," "Hairspray," "Across the Universe." Those titles indicate just how much the concept of "movie musical" has changed. If John Travolta dancing in a house dress works, why not Georges Seurat painting in the park? *