American Cinematographer - August 2008 - (Page 61) Left: In a cavern full of sparkling diamonds, Trevor cautions his companions about the ground beneath their feet, which suddenly shows signs of instability. Below: Plant and animal life becomes increasingly bizarre as their journey progresses. In this scene, the trio is dwarfed by some towering mushrooms. Not many creatures in nature must do that! It’s one of many film-related factors that can contribute to eyestrain during 3-D presentations.” The filmmakers used Sony HDC-F950s, which are designed so that the optical block and the lens can be separated from the rest of the camera. “They can be used to create a very low-profile rig,” notes Brevig. “Other cameras — the Sony F23, for example — don’t come apart, so it’s not as convenient to throw a pair of them onto a Steadicam.” Stereo imaging is a simulation of the way human beings view the world: through two eyes slightly offset from each other. This gives each eye a slightly different perspective on the scene. To re-create that sensation of depth, a stereo image is shot with two cameras, one capturing the image for the right eye, the other camera capturing the image for the left eye. When projected, the images are filtered in a way that allows the viewer’s right eye to see only the right-eye image, and the left eye to see only the left-eye image. (For more on the basic principles of 3-D, see AC April ’08.) The two principal adjustments that go into making a stereo image are the interaxial distance (also called interocular distance, or IO) and convergence. The interocular/interaxial distance is the distance between the two “eyes” when the image is captured: the lines of sight of the two cameras. The average interocular distance for an adult is approximately 2.5", but the interaxial distance between the two cameras can vary widely. The smaller the interaxial distance, the smaller the viewer may feel in the context of the American Cinematographer 61
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