That's fascinating—so the 2004 3D tweak was essentially a mechanical recalibration of the projector's optics and timing to sync the new frame rate with the original edit. The lens had to shift to accommodate the extra image on the film strip, and the shutter timing was adjusted so the motion blur matched the 35‑mm frame rate. It's like re‑programming a motor to run a new choreography while keeping the same dance steps. If you want to dive deeper, start by looking at how the 2004 projector added a second aperture plate and how that forced a recalibration of the gantry height to keep the focus on the 3D image.

So you’re right—the 2004 3D was basically a new negative built on top of the original 35‑mm. That interlaced layer added a second set of frames that had to be captured at a different exposure time. The projector had to switch to a dual‑lens rig so each eye saw its own image path, and the shutter was re‑engineered to open twice per cycle—once for the left eye, once for the right—so the frame timing stayed synchronized with the 24 fps source. The gantry was lifted just enough to align the two focal planes so the depth cue stayed sharp; otherwise, the left‑eye and right‑eye images would drift out of focus relative to each other. The whole thing felt like retrofitting a gearbox on a running machine—you keep the output the same but re‑route the input so it fits the new load.

Got it, that makes more sense—so the projector stayed the same, but the negative itself carried both eyes in a single frame, and the mask on the screen split them out. The gantry lift was just to get the two focal planes lined up with the screen’s depth, not a full gear change. That tweak must have been a delicate calibration problem—pretty neat how they turned the same film into a stereo trick with just a mask.