HARRY POTTER
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DVD
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"I'm not a particularly technical cinematographer," Seresin states. "I know as much as I have to, but I'm more interested in the interpretation of the scene." His stance was just fine with the visual-effects department. "A little knowledge can be a dangerous thing," laughs Guyett. "Michael is a very creative director of photography. Because he hadn't had a great deal of experience [with effects], we were able to discuss what we were trying to achieve, as opposed to some technical aspect of how we were going to go about it. It's actually an easier way of working." Burke concurs: "Both Michael and Alfonso are very visual people who are more interested in the reality or believability of something, and less interested in effects-type movies. So we tried to create effects that were seamless."

That goal involved thousands of considerations. One of the first was film stock. Seresin had recently shot several pictures on Kodak's EXR 500T 5298, which he calls "my favorite film stock ever." During tests, the team ran it through the pipeline to a release print. (At that point, Warner Bros. had not yet committed to a digital intermediate, but at press time one was underway at a DI workstation set up in London by Warner's Advanced Media Services department in collaboration with colorist Peter Doyle.) "The concern was that it has a little patina," says Seresin. "Other people call it grain, but I love that patina." By the end, however, Seresin agreed that a finer grain was needed. "Literally within the space of a few days, Kodak phoned up and told us about its new stock, Vision2 [500T] 5218," recalls Seresin. "I was not a big fan of the previous Vision stocks, but 5218 was absolutely brilliant. I loved its blacks." The new stock also integrated well with the Vision 200T 5274 used by the model unit (which shot with an Arri 435 Advanced). Stone tested both stocks and jumbled them up during one screening session. "Seeing them intercut, you couldn't really tell them apart. But when you look at specific things - the dressing on the set, for instance - I felt that the grain was finer still on the 200," which he ultimately chose.

Because 5218 also worked well with bluescreen, it was used on all effects work except for miniatures. This greatly facilitated the integration of elements. "One of the issues we had was that we were going to be mixing effects and non-effects elements on the same sets because of the digital environments," Guyett explains. "Vision2 is a very fine-grained stock, and it seemed to perform well under most conditions. We used it for just about everything. Straight away, it gave us some degree of consistency."

Every bit helped. The mind-boggling complexity of The Prisoner of Azkaban becomes evident when dissecting a single sequence. Though only two minutes long, the "Time-Turner" scene is a tour de force that illustrates the technical teamwork and intricate detail that characterized this production.

Initiating the film's last act, the scene involves a magical device that enables our heroes to travel back in time. The scene begins in the school's hospital ward, where Hermoine shows Harry and Ron her Time-Turner, a small metal disk she wears around her neck. She spins it, and time reverses course by 24 hours. 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."

"Basically, it was done as an 8-fps effect," says Guyett, who worked on this with second-unit director of photography Peter Hannan, BSC. "We did some motion-control movement so we could control the time it took, but essentially, we just did a whole bunch of separate actions that we could break down and turn into 10 seconds on the screen."

Lighting was the key to integrating foreground and background. During the time reversal, lighting changes had to proceed in lockstep. For the actors and hospital set, "we had lights outside the big casement windows set for daylight, moonlight and sunlight, all on dimmers and going through diffusion," says Seresin. These were mostly 10Ks and 20Ks, plus a "moon light" - a 20K HMI on a remote-controlled crane arm. "We also had one electrician handholding a light and walking onto a piece of wood which was on a roller on a pivot, so he could go higher. Very 19th century!

"As time starts going back," Seresin continues, "we did the lighting changes for real. Guys on dimmer boards with split-second timing go through moonlight, dusk, magic hour, late-afternoon sunlight and midday sun." He adds with a laugh, "It happens so quickly it'll probably only be the cinematographers of the world who'll pick up on it."

This progression guided the second unit's background lighting. "But obviously, here the light would have to go backward," notes Burke. "It got very complicated. In fact, it was probably one of the most complicated shots any of us had been involved in."

The model unit also came into play. Because the large Gothic windows reveal glimpses of the school's roofs and chimneys, these had to undergo lighting changes, too. "I'm not sure if they used it," says Stone, "but we did a complicated still shoot of the view that involved cameras covering more than 200 degrees. We did three positions for the sun as it was gradually setting, and three for the moon. Then we built up a stop-frame animation so Tim and Roger had the choice of being able to run time backward or forward."

The sequence then continues with the kids running down the corridor and exiting. "We tried having the kids run at different speeds, but ultimately they went flat out because it was dramatically correct," says Seresin, adding with a laugh, "The Steadicam operator, Alf Tramontin, nearly gave himself a heart attack trying to keep up with these 13-year-old kids!"

The baton is then passed to the CG camera. When it enters the digital world of the clock, it was important not only to mimic the speed of the Steadicam but also match its lens. While most CGI software can replicate the look of different lenses, more fine-tuning was necessary. "Most lenses have a degree of distortion," explains Guyett, "so we're having to model that distortion into the elements we create and add to the original photography. For every lens that's used, we do our own set of calibration and grid tests to understand the particular character of that lens. So if we create something on a 14mm, we can make sure it has the same quality."