Interview with PoA Cinematographer Michael Seresin

American Cinematographer magazine has an in-depth interview with Prisoner of Azkaban cinematographer Michael Seresin. While the article is fairly technical in nature, it does give some insight into the huge task of filming certain scenes for PoA such as the time-turner sequence – click below to read an exceprt:

Around the three friends, nurses and doctors rush backward in time while daylight backtracks to moonlight and then to day. Next, the trio runs out of the hospital ward and down a corridor, then exits frame into a clocktower stairwell. The camera continues straight, proceeding into the clock mechanism, where 20′ gears eight layers deep are grinding away. Weaving between the gears, the camera exits through the clock face, then tilts down to reveal the clock-tower exterior and courtyard 100′ below. There, below some flying ravens, we see the kids rush across the yard.

Creating this sequence meant linking a Steadicam live-action camera to a CG camera and then to a motion-control camera. “And it all had to feel like one continuous move,” adds Guyett. The first part of the sequence involved a 360-degree Steadicam shot on the hospital set in Leavesden Studios, where most of the sets were located. Half the hospital ward was dressed; the other half was bluescreen. The shot begins facing one direction, with the set in the background. As the dialogue proceeds, the camera circles the trio, moves in to reveal the Time-Turner and then pulls back, facing the bluescreen. When time turns backward, Harry and his friends are filmed at 24 fps in the foreground, while in the background, four hours of hospital action is compressed into 10 seconds of time-lapse footage run in reverse. “Once we got the foreground, we were able to choreograph all of the background action” says Guyett. Adds Burke, “We had to work out a lot of mathematics to figure out how long it would take.”