Honesty compels me to admit I screened La Danse on DVD. But inasmuch as the Reading Gaslamp, which opens the film on Friday, has taken to projecting some of its “alternative” fare on disk, the point might be moot. I can’t say for a certainty that that’s how this film will be shown to the public. I only have my suspicions. With that caveat, this privileged peek inside the Paris Opera Ballet — more than a peek, a thorough probe — ought to be catnip to anyone interested in classical and modern dance, or for that matter in artistic creation in any form, the process of bringing execution in line with conception. Veteran documentarian Frederick Wiseman provides no narrative thread and no commentary from within or without the picture frame, just random drop-ins on rehearsals (predominantly), polished performances, conferences in the inner sanctum, costume and makeup departments, the cafeteria, the corridors, anywhere and everywhere, down to the lone custodian picking up trash in the baroque auditorium. At over two and a half hours, it would be difficult to say that it couldn’t have been tightened. Illuminating as it all is, it would be equally difficult to say exactly where it could have been tightened. Honesty again compels me to admit I watched the two disks at separate sittings.