Camera Developments
May 1, 2010 12:00 PM, By David Austerberry
The rise of the rig for DSLRs and stereo
Shown here are a Canon DSLR body and Nikon lenses fitted to a Kinomatik MOVIEtube PR rig.
Television cameras have added new features over the years at an orderly pace. Once CCD and CMOS sensors replaced tubes in video cameras, the developments have been incremental. The most recent step change has been the migration from recording on 1/2in or 1/4in tape to solid-state, optical and hard disk drives.
Today's typical HD broadcast camera features three 2/3in CCD sensors and an optical beam splitter. In the quest for lighter, smaller and less expensive cameras, manufacturers also offer 1/2in sensors for field production and ENG, as well as 1/3in or even 1/4in sensors for the semipro user with a limited budget.
What distinguishes broadcast cameras from semipro cameras varies. At one time, the tape format was the deciding factor; if it was miniDV, it was a consumer camera.
Expect a broadcast camera to feature an interchangable lens and record at higher data rates than the typical 25Mb/s for low end devices. But for applications like news and observational documentaries, the distinction becomes blurred.
Digital cinematography has evolved along a different route from television cameras. The need to use 35mm cine lenses has led to the adoption of single sensors, with an overlaid color filter array (CFA) rather than the beam splitter and separate RGB sensors. The signal from the sensor is demosiaced derive the RGB color channels.
The use of a single sensor is also the norm for the digital SLR (DSLR) still camera, but save for consumer camcorders, the three-chip approach has dominated the television market. Why do the film guys want the single large sensors? Apart from compatibility with their favored film lenses, the larger sensor delivers two important characteristics:
- Higher sensitivity
Larger pixels gather more light. In the language of film, the sensor is faster.
- Smaller depth of field
The latter characteristic enables the differential focus effects used by cinematographers to define the object of interest in a scene. It also allows the background to be rendered out of focus, useful with fast pans at 24fps. Television cameramen have resorted to wide aperture prime lenses to reproduce the same effects with 2/3in sensors.
This year, a revolution has occurred amongst cameramen, driven predominately by the use of the DSLR.
News agencies
Newsgathering budgets have been under pressure. In addition, news runs 24 hours a day for some networks. Under the pressure to shoot more material without increasing costs, crews have become smaller. A photographer may be sent on a job with a full still camera kit for newspapers and a video kit for television news. Agencies realized that if a still camera could also shoot video, then one person could send back still pictures and video. The cameraman would only need one set of lenses and type of camera body. In response to this requirement, some consumer DSLR manufacturers have added to their cameras the capability to shoot video and to capture associated audio.
Front and side views of an Element Technica mirror rig show how the direct view camera can be moved laterally to vary the interaxial spacing.
It didn't take long for video cameramen to realize that such a DSLR also provided a low-cost way to shoot film-style, with a small depth of field. Does this represent the Holy Grail, the end of the television camera? The answer is no, as there are some catches. First, the audio capability of a DSLR is rudimentary. At best it can be considered cue audio. Second, the reflex viewfinder doesn't work with the mirror up for continuous shooting. Instead, the rear LCD screen is the only viewfinder, and it is difficult to see in direct sunlight.
The sensor may have 10 million to 15 million pixels, far more than the 2 million pixels of a 1080-line television camera. The optical low-pass filter that controls spatial aliasing in the sensor is designed for the higher resolution still capture. As a consequence, HD resolution images will suffer from more spatial aliasing than a video camera designed specifically for HD capture.
Although DSLRs can capture RAW (unprocessed high bit-depth) files in still picture mode, for video capture, an eight-bit codec is used in current camera implementations. That reduces the possibilities for color grading in post without introducing posterization effects.
Some manufacturers have responded to user demands and added to the frame rates that can be used, including 23.98fps, 25fps and 29.97fps. Other manufacturers stick with a single rate, often 24fps, which must be converted in post.
However, a whole industry has grown up supplying add-ons to DSLRs for videographers. A hood and eyepiece can be used to shield the rear LCD panel from ambient light. Although a small depth of field is a desired feature, it necessarily adds to the problems of accurately focusing the subject. Several companies make follow-focus systems to aid focus.
One approach to audio capture is to add a separate audio recorder. Cameras do not record time code, so editors must resort to older techniques like the slate/clapper to ensure audio sync. There is even software that can automatically align the separate audio recording with guide audio recorded in the camera body.
Once focus and audio are under control, then it's time to add camera support and a matte box, and the DSLR body has become a video camera. However, issues still remain, such as battery life and possible overheating. These camera bodies are not designed for long duration shots, and the electronics can get very hot in prolonged use. Manufacturers warn that it may be necessary on occasions to power down the body while it cools. Regular batteries will have a short life, and any shoot will need a stock of fully charged battery packs.
So why use a DSLR with all those drawbacks? It's all down to the creative possibilities for shooters who cannot afford to rent a digital cinematography camera. Already these cameras have been used to shoot prime-time programming. Television camera manufacturers are responding to this demand, and at NAB, two lower-cost, single large sensor cameras were previewed for future release. These will, of course, include proper viewfinders and audio recording facilities, so the current rigs may be short-lived.
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