THOM CALABRO /
07.01.2011
Originally featured on BroadcastEngineering.com
The making of a stereo 3-D lens
Innovations in 3-D stereoscopic lens design, such as automation, lead broadcasters into the future.

Despite the impressive number of movies and TV sports events produced in stereo 3-D, stereoscopic 3-D production remains a specialized, niche application. All of the 3-D stereo lenses are handcrafted and custom made. The glass must meet strict technical and quality control standards. Telephoto lenses for stereo 3-D need to perform according to precise tolerances at every focal length.

During the manufacturing process, the best HD lenses are selected and further modified for stereo 3-D. Many stereo 3-D cinematographers have been using custom-modified versions of Premier HD lenses on such live stereo 3-D productions as the 2010 World Series, the 2010 U.S. Open tennis tournament and the 2010 Major League Baseball All-Star Game. Performance standards and characteristics have been developed in collaboration with directors of photography on the cutting edge of stereo 3-D, such as James Cameron, as well as with stereo 3-D camera rig manufacturers, such as Vince Pace.

As part of the manufacturing process, user feedback is carefully considered from those who have used stereo 3-D lenses in the field to further perfect the lenses or modify them for specialized applications. For example, lenses have been modified for stereo 3-D aerial camera rigs, such as “cable-cams” that fly over a stadium during a sporting event. HD ENG long-barrel lenses are typically modified for use in conventional stereo 3-D camera rigs. And specialized camera rigs intended for aerial or underwater use require much smaller lenses due to space constraints.

First and foremost — lens design

When addressing the best practices for 3-D lens production, it all comes down to making the best possible 2-D lens. The most important part of this process is the design. The design must be sound. The optical and mechanical elements of the lens have to meet strict design criteria. Once the design is finalized, it's turned over to the factory. Once work starts in the factory, the goal is to manufacture the product to the strictest possible standards of the design.

With lens design, there are significant challenges at every step along the way. Manufacturers combine optical, mechanical and electrical components, expecting high performance from the complete package. No other product in our industry is as complex.

One of the more important steps in lens construction is the coating process. Multilayer coatings are comprised of minerals that are deposited on each element of a lens. Considerable care must be taken when coating a lens. The coatings produce a number of effects. They allow for greater light transmission than an uncoated element, thus providing the lens with a lower T-factor number. They also reduce the amount of flare and ghosting, giving the lens greater clarity, contrast and depth.

Made to order

While stereo 3-D lenses are 100-percent handmade, there are some preliminary manufacturing processes that are automated. For example, robots handle the processes of coating and grinding the lenses. Once all of the mechanical and electrical components have been assembled, selected HD lenses move on to a specialized workbench where the glass is further refined and polished.

It takes many man-hours to handcraft a single stereo 3-D telephoto lens, with technicians who are experts in optics handcrafting them. Most of the time is devoted to repeated analysis and testing of the lenses, and then putting them back on the workbench for further refinement until tight tolerances have been met.

In the early days of design, manufacturers relied on slide rulers; next came calculators and then computers. Each step allowed lenses to be built with tighter tolerances. Recently, Fujinon developed a software program called Global Optimization (GO) Technology. This program is a tool that simultaneously monitors many design parameters, affording designers the ability to build a lens that is better optically as well as lighter and smaller. A couple of years ago, the company introduced the XA88x8.8 field lens, a replacement for the XA87x9.3. The XA88x was not only longer and wider optically than the XA87x, but it was physically lighter and smaller. The design of the XA88x field lens was a direct result of the GO Technology program.

Some lenses are not ideal for 3-D production. Very long lenses would not be well-suited. The images that these lenses shoot are from a distance, which would make the image appear very flat or compressed. Thus, a 3-D image would be hard to capture using a conventional rig. It is possible to do, but the lenses would have to be mounted far apart from one another. Recently, a 3-D production was made using long lenses, shooting subjects very far away, namely the moon and distant stars. The 3-D effect was only realized because the lenses were mounted hundreds of feet apart.

Many technical challenges

While the lenses are typically mounted on two cameras within a specialized stereo 3-D camera rig, stereo 3-D lenses are not typically manufactured or sold in pairs. Since each lens is manufactured according to strict tolerances, they are virtually identical and interchangeable, providing the precision performance stereo 3-D requires. Production companies and rental houses do not have to worry about mismatching lens-pairs, which makes it easier if they are deploying a large complement of lenses.

With stereo 3-D lenses, the optical centering has to track at every focal length. So when a telephoto lens is zoomed from the tight end to the wide end, or vice versa, the center point cannot vary.

In standard production, when a camera operator zooms in on an object such as a face to get a close up, it's possible to experience a slight optical shift where that object shifts away from the center of the frame — maybe up or down, or left or right. The operator compensates for this, shifting the camera slightly to recenter the object.

But if this optical shift happens with the lenses in a stereo 3-D camera rig, one might cause the centered object to shift to the left, while the other lens shifts it to the right, or any combination of misalignments ultimately detracting from the 3-D illusion. Proper alignment and centering at every focal point must be set at the factory.

Innovative applications

Stereo 3-D lenses are also configured to allow for automation, such as a Synchronous Control box that can synchronize the operation of two lenses in tandem, automatically. If the user needs to know the precise lens position in order to accurately repeat a shot, that information is available as an output. With a RS-232 port on the Synchronous Control box, this system now allows operators to adapt any brand of serial controller they like.

There are also instances where stereo 3-D camera rigs are mounted on jimmy jibs or cranes, or positioned in hazardous locations, such as alongside a racetrack to capture a high-speed race. By adding a wireless controller, all cable connections are eliminated, such as those running from the hand control up to the 3-D camera rig atop the crane. Operators can then control the lenses from a distance of up to 100m away, including from inside a nearby mobile unit.

In the future, expect to see increased demand for stereo 3-D lenses, especially for events like the Olympics and World Cup. Stereo 3-D is also proving especially beneficial to such sports as boxing and on golf putting greens, where the action is confined to a relatively small area. During the 2011 Masters Golf tournament, there were more than 20 3-D camera rigs with lenses on the greens, enabling viewers to detect how the contours of the course might affect the way the ball would travel.

Thom Calabro is director of marketing and product development at FUJIFILM North America, optical devices division.



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