American Cinematographer - April 2008 - (Page 60)

Fig. 10: Linear Polarization Fig. 11: Linear Polarization Illustrated Fig. 12: Circular Polarization Fig. 13: Circular Polarization Illustrated Fig. 14: Active Glasses then cut directly to an object in front of the screen. The average viewer will have difficulty converging the suddenly “close” object, to the point where he might see double images for several moments. Experienced viewers of 3-D films won’t have this problem, and this can lead to mistakes if you happen to be part of the creative team involved in a 3-D production. If you work extensively in post for 3-D movies, you become more and more adept at quickly converging disparate objects. However, your audience won’t have the advantage of exercising their eyes as much as someone working on a 3-D film. If this disparity isn’t taken into account, the resultant movie can cause problems for the audience. The filmmakers will have no trouble watching it, but the average viewer will find it difficult to converge 3-D images that cut between extreme positions in front of and behind the screen plane. Some 3-D films attempt to guide the viewer to converge objects in front of the screen. They do this by slowly bringing an object closer to the audience, allowing viewers to track the object as it comes farther and farther off the screen. The makers of the theme-park attraction Captain EO accomplished this with a shot of a floating asteroid that comes off the screen at the beginning of the film. In Muppet*Vision 3D, the effect is created with the simple gag of a “3-D” logo positioned at the end of a broomstick that is pushed into the audience’s face; the effect is repeated at the end of the film with the shot of Kermit perched at the end of a fire-truck’s ladder. In T2 3D: Battle Across Time (AC Aug. ’96), Robert Patrick’s molten head slowly comes off the screen toward the audience. Creating the illusion of true stereoscopic imaging requires that the left eye and right eye see unique left/right imagery. This is achieved with various kinds of glasses that perform the task for the viewer. It should be noted that all 3-D glasses — and projection systems — have an impact on the brightness of the projected image, generally a light loss on the order of 3-4 stops. The first public use of polarized glasses for a 3-D motion-picture presentation took place at the 1939 New York World’s Fair. Called linear polarizers, these glasses work by orienting the left- and right-eye polarizing material at right angles to each other. Though this is not actually visible to your eye (Fig. 10), the effect is graphically illustrated in Fig. 11. In this system, the left- and right-eye projected images are each projected through linear polarizers that match the orientation of the glasses. This method is effective at separating the left and right image material; however, if the viewer tilts his head at an angle, there will be “leakage” of the image information, allowing the viewer to see both images simultaneously, which, of course, is not ideal. Polarizing glasses, and all glasses that do not require any electronics in order to function, are called “passive glasses.” Polarized 3-D presentations always require projection onto a silver screen in order to maintain polarization of the projected image. Glasses that employ circular polarization look just like their linear cousins but perform quite differently. A simple explanation is that circular polarization can be oriented in clockwise and counterclockwise directions. The left- and right-eye projected images are polarized in opposing circular-polarization orientation, as are the respective lenses on the glasses. The circular-polarization effect is not visible to the eye (Fig. 12), but is graphically illustrated in Fig. 13. A principle advantage of circular polarization is that the integrity of the left-/right-eye image information is always maintained, no 60 April 2008 Polarization illustrations by Rob Hummel. Polarizing glasses courtesy of RealD.

Table of Contents Feed for the Digital Edition of American Cinematographer - April 2008

American Cinematographer - April 2008 Contents Editor's Note Global Village: The Counterfeiters Short Takes: Milia Production Slate: Paranoid Park Production Slate: All the Boys Love Mandy Lane Card Sharks Temple of Doom 3-D Cinematography Sundance 2008: Mining for Movies Post Focus: Digital Film Tree Gets into Peyote Post Focus: FotoKem’s 3-D Workflow Post Focus: Technicolor Digs in at Pinewood Filmmakers’ Forum: Steven Fierberg, ASC on Searchers 2.0 New Products & Services International Marketplace Classified Ads Ad Index Clubhouse News ASC Close-Up: Rodney Taylor

American Cinematographer - April 2008

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