thin layer of snow fell within it one humid morning, so the characters' breath would be visible. Since the set lighting warmed the air, it could only remain cold enough to film for three minutes at a time. It broke down frequently, and Friedkin was only able to complete five shots each day; the complete scene thus took a month to film, in continuity, the order they were written in the script. Originally it was hoped that the room would not have to be chilled that much. But while the actors' breath was visible at just below freezing, the set was too quickly warmed by the filming equipment. Going down to worked, but according to Roizman Friedkin decided on the maximum in order to improve the actors' performance. "An actor on his knees for 15 minutes at 20 below zero is really going to feel cold. It worked out very well." Once the actors' breath appeared, it was necessary to backlight the actors, which while it is easy enough to do in still photography is much harder when filming a movie. "[W]ith the actors moving all the time, it got to be a bit difficult. It was always a matter of finding a place to hide the backlight and finding a way to keep it off of the actors", Roizman said. Blair wore green contact lenses meant to give her eyes a bestial appearance for scenes when Regan is possessed. To accentuate them, the crew used a soft light with its barn doors nearly closed to throw a narrow strip of light across her eyes. "It's probably a 75 mm lens, because we used that a lot", Friedkin recalls. It was easier to film some of the other supernatural manifestations, such as the bed rocking and the curtains blowing, in Regan's room, since the walls and ceiling of the set were wild, or capable of being moved to accommodate a camera; after the scene where the ceiling cracks it was necessary to use a hard one. A hole was cut in the ceiling for the rig to go through when Regan levitates as the priests chant "The power of Christ compels you!", the most challenging shot in the sequence. the Blair wore a bodysuit under her nightgown with attached hooks for monofilament wires. Roizman said that while he had filmed similar scenes in television commercials, painting the wires to match