'THE EXORCIST' shot this before the Steadicam existed: key grip Eddie Quinn hung a seat from ceiling tracks, and an electric hoist lifted operator Enrique Bravo up the stairwell in step with the actors.
Since the camera saw almost 360°, Owen Roizman lit the whole stairwell through a muslin ceiling so the rig cast no shadows.
Wow, that shot from The Exorcist still gives me chills. I've always wondered how they achieved the eerie atmosphere, was it mostly lighting or camera angles?