I very much planned today’s expedition to see Harry Potter and the Order of the Phoenix as an experiential field trip. I’m a fan of the books, have been speeding my way through #7 (Deathly Hallows), and would have seen the film of #5 in any case. But it happened to be playing near me on an Imax screen in 3D. The last movie I saw at an Imax theater was The Matrix Reloaded (2003), and though I noted last year’s release of Superman Returns in Imax 3D, the general awfulness of the 2D, economy-sized version of Bryan Singer’s weird waxwork tribute was enough to keep me from going. But Order of the Phoenix is getting strong reviews, and I wanted to sample this latest in high-tech visual splendor.

I already knew that, as with Superman Returns, only a portion of Phoenix would be 3D. What surprised me was how explicitly this was made clear to spectators, both as a matter of publicity and in ad-hoc fashion. Warnings were taped on the ticket window: ONLY THE LAST 20 MINUTES OF HARRY POTTER ARE IN 3D. The man who tore my ticket told me the samew thing, in a rote voice, as he handed me the yellow plastic glasses. As the lights went down, a recorded announcement reiterated the point a third time, except in a tone of awe and promise: “When you see the flashing icon at the bottom of the screen, put on your glasses, and prepare to enter the spectacular world of Harry Potter in an amazing action climax” was the gist of it.

All this tutoring, not just in the timing of the glasses, but the proper level of anticipation! Calibrating the audience’s reactions, indeed their perceptions, stoking the excitement while warning us not to get too excited. It went hand-in-hand with the promos for the Imax format itself, playing before the film and describing the awesome fidelity and sensory intensification we were about to experience. It seemed odd that we needed such schooling; aren’t 3D and giant-screen technologies about removing layers of mediation?

But of course that’s naïve; the most basic theory of cinematic spectacle reminds us that special effects (and Imax 3D, like sound, color, widescreen, and other threshold bumps, is a kind of meta-special-effect, an envelope or delivery system for smaller, more textually specific clusters of effects) function both as enhancements of illusion’s power and as a reminder of the technology involved in bringing the illusion to us. At the movies, we’re perfectly capable of believing in what we see while also believing in (and celebrating) its constructed nature; this is as true of special effects as it is of the editing that strings together a story, or our perception of Albus Dumbledore as being simultaneously the headmaster of Hogwarts and a performance (of subtle strength, in this case) by Michael Gambon.

And we do need the calibration of expectation, the technological tutoring, that frames the Imax 3D experience, as demonstrated by the woman buying tickets in front of me who asked, “What’s Knocked Up? Is that 3D? Do you have a list of which movies are 3D and which aren’t?” I’m not mocking her: in our imaginations, all movies are 3D, in the sense of possessing a life beyond the play of light and shadow, in the sense that all media “realities” are to some extent already “virtual.” The interesting thing right now is that the technological assist provided by 3D is so prohibitively expensive and labor-intensive that only short sequences – those corresponding, as in Order of the Phoenix, to climactic stretches of action – enjoy it. For the moment, 3D is a sharply bordered land within the larger imaginary domain of movies. Like any border crossing, there must be signposts to let us know when we are entering and leaving the territory.

What of Phoenix’s 3D itself? I sure got a kick out of it – that final 20 is fantastic in dramatic terms, and as critics have pointed out, it’s designed perfectly for spatial amplification. I had tears in my eyes by the end of it, but partly this was due to the strange nostalgia the 3D experience brought out – nostalgia for all the promises movies make, whether in 2006, 1956, or 1906: each era offering its technological tricks so eagerly, convinced of its charms but taking time to warn us not to get too excited, lest we be disappointed and never return.