Magazine article American Cinematographer

Filming 14 TV Monitors Simultaneously without Shutter Bar, Roll Bar or Visible Splice Lines

Magazine article American Cinematographer

Filming 14 TV Monitors Simultaneously without Shutter Bar, Roll Bar or Visible Splice Lines

Article excerpt

A highly technical, but effective, way of eliminating a problem that has plagued cinematographers since the advent of television

In shooting the movie CITY ON FIRE, a Sandy Howard Productions/Astral Bellevue production, the script called for photographing many television monitors (as most of the action takes place in a television control room) and various television sets. The feeds were to be prerecorded and/or live. Their preliminary tests failed to eliminate the problem of shutter bars occurring on the monitors and television screens, a problem which has long plagued cinematographers.

Sandy Howard called on Sonex to solve this age-old problem of photographing a monitor ortelevision set with a motion picture camera, while still retaining clear, stable television images with good color quality, and with no shutter bar, roll bar, or visible splice line.

In the past, the problem was solved generally by an optical technique called a burn-in. This, however, has several drawbacks. The most restrictive drawback is that the motion picture camera must be locked down and, in order to keep costs down, talent must not cross in front of the TV screen. Also, the audience usually senses that the picture is not real.

In CITY ON FIRE, since 14 different TV pictures had to be photographed simultaneously in the scene, the optical burnin was considered impractical.

Upon arriving in Montreal, I found that some of the material to be used was on 3/4" U-matic cassette, some of the material had been photographed on 5247 and the print transferred to 2'' video tape, and some of the material was to be live and off of television chains. Upon examining the 3/4'' material, I discovered that some of the recordings had been shot outdoors without an 85 filter, but with a portable color television camera that had been balanced for 3200°K.

Canada, as well as the United States, is on the NTSC color television standard. This means that the television picture derives its timing from a sync generator. This sync generator has a master crystal oscillator operating at 14.318180 MHz. The crystal is kept at constant temperature in a crystal oven and its frequency has an accuracy better than .0001%. Some stations, like the networks, have a more accurate Rubidian standard and some even have atomic clocks with accuracy directly traceable to the National Bureau of Standards and are occasionally used as timing references by the military, NASA, JPL, etc.

This 14.3 MHz crystal is divided by 4, producing a 3.579545 MHz subcarrier. This subcarrier will, upon encoding, contain the color difference signals. The frequency 3.579545 was chosen to be an odd multiple of half the TV line frequency so that it would interlace with the TV sound carrier and prevent an annoying moiré. The 14.3 MHz crystal oscillator is also divided by 455 to produce a frequency of 31.468 KHz. This is used to produce equalizing pulses during the vertical interval to interlace field 1 information with field 2. This 31.4 KHz is further divided by 2 to produce a 15.734 KHz scanning frequency. The 31.4 KHz equalizing pulse frequency is divided by 525 producing a field frequency of 59.94 Hz. The field frequency is twice the television frame rate of 29.97 frames per second.

This 29.97 frames per second is typically referred to as 30 frames, but in actuality is only 29.97.

The motion picture camera in this country runs at 24 frames per second. In other countries it might run at 25 frames per second. Principal photography on CITY ON FIRE was photographed at 24 frames per second, using Panavision equipment.

To shoot the control room and studio scenes and the TV sets, I modified a BNCR camera to run at 23.976 frames per second or 4/5 of the television's 29.97 frames. This was done electronically by taking the 59.94 Hz field frequency and generating from these pulses a sine wave of 59.94 Hz that could be phased ± 200 electrical degrees with respect to these pulses and amplifying the sine wave up to sufficient power to drive the BNCR with a full load of film. …

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