The happiest 15 minutes in the history of cinema really pop off the screen in the new 3D IMAX conversion of “The Wizard of Oz.” Those minutes, coming as Dorothy Gale (Judy Garland) steps into the Technicolor wonder of the Merry Olde Land of Oz, are as giddy, goofy and gloriously kitschy as ever.

And thanks to 3D and digitally cleaned-up copies of the film, the details are nothing short of stunning, even if the depth of field isn’t improved much from when Victor Fleming pointed the camera at those sets 75 years ago. The sheen on the fake plants shimmers and the stitches stand out in the burlap face of Scarecrow Ray Bolger.

Garland’s wise-beyond-her-years crooning, full of longing in “Somewhere Over the Rainbow”; Frank Morgan’s tour de force supporting work (five different roles) as Professor Marvel, the Wizard and others; Bolger’s rubber-legged genius — the virtues of this masterpiece are as obvious as ever.

The improved texture was reason enough to convert this to 3D. The original sepia-toned opening and closing are intact and the Wicked Witch’s gnarled green hands seem to poke through the screen.

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The witch-arrivals, in clouds of red smoke, are still primitive (you can see the trap door), and the whole thing looks and sounds like a product of its era. But with “The Wizard of Oz,” the passing of the years merely adds to its charm.