American Cinematographer - April 2011 - 56

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Optical Filtration and 3-D

Screen Plane’s Production Rig allows multiple arrangements for using effects filters on the mirror box. Shown here are two 4"x5.65" filter trays.

viewing-angle issue. Now, working with Omega Optical, Panavision has introduced a 3-D theater system, using filter technology that breaks the spectrum into 10 bands of light, another approach to obtain more vibrant color. There are yet other twists on the above techniques, but let’s now see what’s involved with actually making the images in the first place. The most basic capture method for producing 3-D is to use two cameras side-by-side, emulating the positions of human eyes. There is a whole science built around this concept — on how we see depth, and how that can be manipulated by adjusting the distance between the lenses (the “interaxial distance”) and their angle of convergence — to accommodate the many storytelling requirements encountered in modern production. This has resulted in the development of two distinct types of camera layouts. One is the basic side-by-side; two camera systems with matched
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lenses are mounted together so that convergence, focus, zoom and other functions can be readily coordinated. (This works especially well for sports because the subject is generally at a distance.) With this setup, effect filters mounted in the usual way on each lens are easy to use as long as both match. This design suits a wide range of situations. The Panasonic AG-3DA1 series fits two camera systems with matched lenses into one housing, simplifying synchronized control of zoom, focus and more, making 3-D capture easy. The lenses in the AG3DA1 have a physical size that prevents them from positioning the interaxial distance close enough for proper convergence on subjects closer than 2.2 meters (7.2'). This precludes shooting within the range of camera-to-subject distances that require the lenses to be positioned closer together than they physically can be. For that, we have the beamsplitter rig. The concept behind the beamAmerican Cinematographer

splitter rig is like a Teleprompter. A special mirror, transmitting some of the light and reflecting some, is positioned at a 45-degree angle in front of the two camera lenses. However, instead of being positioned side-by-side, the “direct” camera views horizontally through the mirror, and the other camera is mounted vertically, either above or below, viewing the mirror’s reflection. This makes it possible to bring the interaxial distance as close as needed, even to the point of overlapping. This solves a key problem with the side-by-side camera arrangement, but in doing so it introduces a whole slew of new ones, some of which are tricky to handle. Peter Anderson, ASC, one of our most prolific 3-D cinematographers (U2 3D, Captain EO), walks us through the physics of the beamsplitter, highlighting the attendant difficulties it presents: “Let’s take the direct camera. Using a moderately wide lens, the top of the lens is looking through the glass,

American Cinematographer - April 2011

Table of Contents for the Digital Edition of American Cinematographer - April 2011