A new mirror rig is designed to support existing and upcoming HD and digital cameras for 3D.

The Gemini is a new 3D, large-format camera designed by Martin Mueller, a co-founder of MSM Design (Hayden Lake, ID), to be small, fast, and lightweight while retaining the image quality expected in giant screen films. It is a completely original camera designed from scratch as a 3D camera. The Gemini can be loaded with film, put in a medium-sized pelican case, taken anywhere, pulled out of its case for shooting quality 3D in seconds.

The Gemini photographs a 24mm x 36mm stereo pair onto two strips of 35mm film. Each ‘eye’ has eight perforations, double the size of a full-aperture, 35mm motion picture frame. To make up for the smaller than 15/65 image size, several steps were taken:

First, the film movements incorporated a vacuum back and an ultra steady design that allows the camera to outperform 65mm cameras over a given image size. Due to the large image area of 65mm film, even with a vacuum back it will shift slightly in the camera’s gate, reducing the resolution of the image being exposed. 65mm cameras typically resolve 40, at best 50 lines per millimeter in the center of the image. Second, the optics used in 65mm cameras have not kept up with the improvements in lenses for 35mm formats, so that smaller formats now have sharper lenses. With these improvements, the Gemini is able to capture 80 lines per mm, which makes up for most of the smaller image size. There are also image improvements in post production, but even before those enhancements the Gemini has a resolution that is three times that of a full HD camera.

One essential feature was a 2.5- distance between the lens centers, as ninety percent of giant screen 3D photography needs to take place at that value. Mueller used wider inter-axials but usually on longer lenses with wildlife whose scale is more forgiving. Using wider inter-axials in tight shooting environments can be disastrous.

The first challenge in Mueller’s Gemini 3D camera was to see if he could get the film to run horizontally though two 8/35 movements at such close spacing. Film in a motion picture camera spends most of its time standing still, capturing each amazing image then waiting for the shutter to close completely. When it moves, it has to move fast. At the normal 24 frames per second, the loop of film through the movement sees peak accelerations of 110 g’s and speeds over 1,000 feet per minute.

The versatility and usability of a camera has a lot to do with its size and weight, where smaller equals lighter equals better. The next challenge was the camera’s magazine layout. Meuller knew that to keep the magazines small, he wanted to arrange the rolls vertically and on the same center (coaxially). This meant finding a simple way to get the film turned 90 degrees to go through the camera and then back 90 degrees to wind up on the take-up. The arrangement had to be easy to thread, and had to move the film safely.

To keep the magazine weight down, Mueller chose to keep the magazine motors in the camera body. The necessary mechanical drive to each spindle is through a neoprene toothed belt that wraps itself around the drive pulley as the magazine is mounted to the camera. The electrical connections are engaged at the same time. To insure a solid connection, there is a deadbolt style lock for the magazine which connects its frame directly to the baseplate of the camera.

The operators’ lens control concept was also unconventional. The control sends the exact position of the focus, iris, and convergence knobs to the camera. These numbers define the drive motor positions for those functions. Each lens has its own tables in memory, and identifies itself to the camera as it is mounted. Three motors then drive the lens pairs to the requested positions.

“We used 5 Litton brushless motors to move film, and three Faulhauber gearmotors to move lenses, all with HEDS encoders,” says Mueller. “It worked great in the shop, but on the second shoot, electrical noise sneakily added counts to the focus knob number causing a corresponding focus drift.”

Mueller rewired the control with noise immune encoders and added a digital readout which independently confirms the actual lens response in feet and inches for focus and convergence, or f/stops and tenths for aperture.

“Software control of camera functions has allowed features we only dreamed of on earlier cameras” he says. “In addition to the complete camera and lens remote control, we have very precise control of camera speed and film tension in the magazines, integral time lapse functions, footage remaining displays, and anti-tailout protection.”

A speed ramp can be coordinated with aperture compensation, or convergence slaved to a focus pull. The camera can readily interface to motion control systems or passive encoding for visual effects.

Mueller also uses the compact DMC-2183 8-axis Ethernet controller from Galil Motion Control to produce the precise coordinated motion requirements of the Gemini 3D camera. He programmed two pairs of axes (1–2, 3–4) to control camera film magazines.

The Gemini camera was designed to shoot images that would enter a digital pipeline. Digital mastering is no longer the future of giant screen 3D films, according to Mueller. “It has become the present,” he says. “Its ability to perfectly match and align stereo pairs has made it an essential component of good 3D filmmaking. Digital mastering adds creative options that filmmakers in all formats now require.”

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