It was the end of a 4 hour filming flight of Auckland's North Island, when pilot Tony Monk reported seeing Dolphins below, so with that we swiftly dove to an elevation of 20 feet and began the chase.

Fortunately I was using the Cineflex stabilised gimbal fitted with the Sony HDW950 camera, so by the time we were alongside the swiftly swimming Dolphins the camera was rolling, exposure and focus was set. But where would the dolphins surface next... with tape rolling we waited and pow!, a precision display of aquatic acrobatics as five dolphins carved perfect arcs across frame.

A beautiful moment recorded on HD, this could sum up most of Tony Monks recent shooting experience as he runs the only remote head HD gyrostabilsed camera in the world at Heletranz the Auckland based helicopter charter company.

Heletranz have operated a standard def stabilised camera platform from the mid nineties ably operated by cameraman Peter Thompson who has had more filming hours in the air than some pilots.

The HD gimbal was built to Tony's specification by Cineflex of Lincoln California. Tony wanted a smaller unit, interchangeable lenses and a shipping weight that would enable the kit to be shipped as excess baggage.

No case could weight more than 32 kilos.

John Coyle of Cineflex did what many have been trying since the birth of HD, that is to devise a means of conducting a HD signal without the use of cables. He also devised a straightforward way of changing lenses on location without upsetting the delicate balance of the system and remarkably, the flight cased weight of the gimbal came in at under 32 kilos.

It is also smaller than the standard def system at a very compact 14.5 inches in diameter. A smaller ball means the helicopter can fly as it was designed, it is faster and more manoeuvrable than film gimbals.

The pictures are remarkable. They are probably the steadiest airborne pictures to date. Tony Coyle states that the zero intra frame movement that is a hallmark of HD raises the bar of gyro systems. Systems designed for film cameras need not be stabilised to the same degree as HD because the intra frame movement common in film cameras combined with varying grain pattern disguises very high frequency vibration. With HD a vibration that is half a pixel height will reduce resolution by 50%. The smallest vibration is easily spotted on HD.

The true test is to watch the images on a digital projector. I did just that, using the JVC D-ILA projector at native 1920x1080 resolution onto a 20 foot screen. The images displayed no vibration even when viewed at point blank distance from the screen.

For this reason compositors are beginning to turn to HD for use as background plates.

So how does a gyro gimbal work?Well, spinning mass gyros have been around for decades. They create a great deal of inertia within a soft drink can sized package, by spinning heavy tungsten wheels at tens of thousands of revolutions per second. If a camera is balanced on its centre of gravity and then gyros attached any minor vibrations are absorbed by the gyros. The disadvantage of this system is that they are bulky and the gyros can be toppled by a heavy bump or fast pan.

The newer systems rely on sensors to detect vibration and instantly input a correction to the camera. So when the sensor detects say three bumps from the left it inputs 3 counter bumps to the camera to move it to the right. So even with a 800mm lens the subject stays stationary in frame.

The positional resolution is 0.001 degree.

The system also has its own kind of internal inertial guidance system. Point the camera at a stationary subject and the camera remains pointed in that direction, virtually regardless of the orientation of the helicopter.

It takes a few minutes of sharp turns before the internal system looses track.

The gimbal is small because it houses just the lens and ccd block of the camera, a Sony HKC-T950 block adapter. The body of the HDW950 camera is inside the aircraft. The camera has a similar menu to a f900 camcorder and shares the same ccds. It is capable of all frame rates including 720p. Until a portable recorder is available a f500 HDCAM earns its air miles in the cargo bay. The new small Sony SR format portable recorder is a obvious contender, offering slightly increased resolution, much needed as the HDCAM compression is by far the weakest link in the HD gyro chain.

The system will accept the 4:4:4 camera whenever it becomes available and when hooked up to the SR recorder there will be more scope to grade in post.

Finer details will be better resolved making large screen projection of images even more engrossing.

Lens available are Canon 11x4.7, 40 x11, 40 x14 and 21x 7.5.

The compact wide angle lens with its doubler offers a good range in a compact package. It is surprising how good the doubler is, although I have not tested it transferred to 35mm film, it is ok for HD broadcasts.

As is common with "TV" lenses there is a little "ramping" at the long end, a characteristic that film technicians are not familiar with as film lenses need to be constant throughout the range TV lenses do not as there is usually a technician riding exposure.

The lenses have been adapted to fit into the compact package by removing the servo and rebuilding it. Lens changes take about a hour, but can be done in the field, ideally out of the weather.

Monitoring is a bit of a headache, even the best flat screen HD monitor is inadequate to gauge exactly where the depth of field falls off.

Peter Thomson has configured the joystick of the gimbal with a button that operates the snap zoom function on the Canon lenses to check focus.

However it is possible to fly with a 14 inch crt by removing or revolving the front seat.

However, the 2/3 inch ccd has good depth of field that encourages confidence in the operator to go for much tighter frames, especially in uncontrolled situations. Those who crow for a larger image format on HD usually have little experience of the advantages offered by the great depth of field a 2/3 inch imager.

Better control of focus is needed, it is a hard task to pan tilt and operate focus to HD standard. There are no distance marks on the remote focus control because the sytem has evolved from a TV environment. For very critical work John Coyle is developing a set of tools to enable more accurate pull focussing required for a track in to a subject.

The small size of the gimbal puts little pressure on the pilot. The cockpit is a very relaxed environment.

With a clever camera setup it is possible to have forground action whizzing through frame whilst the subject stays sharp. This is not possible on film becuase the foreground action will strobe. This enables a much faster speed at closer proximity to the ground than ever before, offering a new range of shots for the aerial coordinater and DP.

Gaton Charest, a US based Imax producer who used the Helitranz system recently on the 2003 Americas Cup stated;

"We were planning to bring everything with us but if we had used a 35mm gyro camera as originally planned the project would have cost at least 2 million dollars more and not worked as well."

"It was the best I have ever used in terms of quality, stability, sharpness of the picture and the ratio of the zoom I could use. Previously 20X was the maximum I could use and we were going to 40X with great stability, I was quite surprised."

James Cameron also used the same HD camera for the 3D "Ghosts of the Abyss" which was premiered in the Imax format.

It is hard to think of an application where HD excels as much as this, of course a few more stops in the highlights would be useful, not that the dolphins would notice.

The HD gyro is a killer application for HD.

Copyright Michael Brennan 2003

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