Caution: No Two Lenses Are The Same

Fig. 4.7 No two pairs of optical glass are identical.

A key issue that live-action 3D, from sports to feature films, has to contend with stems from the fact that no two sets of glass optics are exactly alike. The slightest inconsistencies in alignment, and distortions and aberrations from lenses, focus, zooming, lens flare, or spherical reflections can produce discomfort or break the stereo illusion. Some lenses even create subtle anamorphic squeezes.

The problem is particularly acute when zooming. According to 3Ality Technica CEO Steve Schklair, since no two lenses track identically, even a fractional misalignment will lead to uncomfortable 3D viewing. The image will not only deviate around the center of the lens during a zoom (horizontally) but also vertically.

Motorized rigs automated by software have been designed to control the interaxial and convergence parameters and to eliminate pitch, yaw, and roll between cameras. Such motorized rigs also ensure that lens length, focus, iris, and zoom (FIZ) are linked as closely as possible.

For live productions where a reliance on post is not an option, obtaining accurate results at source is critical. It is vital that timecode references are genlocked and computer control is established over zoom, interocular distance, and lens length, while each camera’s respective metadata is saved.

New software technologies are being used to calibrate the optical centers of the two lenses throughout the zoom range. After alignment an operator can set the required interocular distance of the rig and software will calculate and correct for any misalignment during production.

Excerpt from Exploring 3D: The New Grammar of Stereoscopic Filmmaking by Adrian Pennington, Carolyn Giardina © 2012 Taylor & Francis Group. All Rights Reserved.

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