reflecting his loneliness. Sets were still used for some interiors such as the Bat Bunker, the replacement for the Batcave, on the outskirts of the city. The production team considered placing it in the penthouse basement but believed it was too unrealistic a solution. Much of The Dark Knight was filmed using Panavision's Panaflex Millennium XL and Platinum cameras but Christopher wanted to film about 40 minutes with IMAX cameras, a high-resolution technology using 70 mm film rather than the more-commonly used format 35 mm; the finished film includes 15–20% IMAX footage, running for about 28 minutes. This made it the first major motion picture to use IMAX technology, which was generally employed for documentaries. Warner Bros. was reluctant to endorse the use of the technology because the cameras were large and unwieldy, and purchasing and processing the film stock cost up to four times as much as typical 35 mm film. Christopher said cameras that could be used on Mount Everest could be used for The Dark Knight, and had cinematographer Wally Pfister and his crew begin training to use the equipment in January 2007 to test its feasibility. Christopher particularly wanted to film the bank heist prologue in IMAX to immediately convey the difference in scope between The Dark Knight and Batman Begins. Filming in Chicago Principal photography began on April 18, 2007, in Chicago on a $185million budget. For The Dark Knight, Pfister chose to combine the "rust-style" visuals of Batman Begins with the "dusk"-like color scheme of The Prestige (cobalt blues, greens, blacks, and whites), in part to address over-dark scenes in Batman Begins. To avoid attention, filming in Chicago took place under the working title Rory's First Kiss but the production's true nature was quickly uncovered by media publications. The Joker's homemade videos were filmed and mainly directed by Ledger. Caine said he forgot his lines during a scene involving one video because of Ledger's "stunning" performance. The first scene filmed was the bank heist, which was shot in the Old Chicago Main Post Office over five days. It was scheduled early to test the IMAX procedure, allowing it to be refilmed with traditional cameras if needed, and it was intended to be publicly released as part of the marketing campaign. Pfister described it as a week of patience and learning because of the four-day wait for the IMAX footage to be processed. Filming moved