Film chain
From AmericolaWiki
A Film chain or Film island is a television - TV camera with one or more projectors aligned into the lens of the camera. With two or more projectors a system of front-surface mirrors that can pop-up are used in a multiplexer. These mirrors switch different projectors into the camera lens. The camera could be fed live to air for Broadcasting through a vision mixer or recorded to a VTR for post-production or later broadcast.
Contents |
[edit] Projectors
The projectors often are: 16mm Film Movie projector, a 35mm Slide projector and a 35 mm film Movie Projector. In low end use the motion picture 35mm projector would be replaced by a second 16mm projector or 8 mm film, or Super 8 mm film or Single-8 projector. The multiplexer with the camera and projectors surrounding it would often be called a Film island. The optical or Mag or Magnetic strip sound track on the motion picture would be picked up by the projector and would be fed to an audio sound Mixing console or to the VTR. See: Sound-on-film, Film Sound and 35mm Sound.
The Slide projector at a TV station would be used for the TV Station’s Logo, the famous “Please Standby By” Slide and some test patterns. Some used a dual-rotating drum slide projector that would have its own mirrors to switch between the drums.
The film Projectors used in a Film chain are not standard. They had special five-blade shutter that is used convert the film’s 24 frames per second into NTSC’s 30 frame per second Video. If this was not used the video would have major flicker problems. This process is called a "3:2" pull down. Modern telecines use the same process, but it is done electronically, not with a five-blade shutter. "3:2" pull down means that a film frame is shown for three TV fields. The next Film Frame is shown for 2 TV fields. The add field in the “3” is used to convert the 24 frames per second to 30 frames per second. A normal projector has a 2 bladed shutter that shows the same frame twice. Before modern continuous motion Telecines, Film chains were sometime referred to as telecines.
All film projectors use sprocket rollers to move the film and a pull-down claws to move and stop the film in the gate. The film is moved in the gate while the shutter blocks the light.
In PAL, SECAM and other 25 frames per systems the film projector is speeded up one Frame per Second to 25 fps. This gives a one-to-one film to video frame transfer ratio. Thus a standard 2 bladed shutter can be used.
See Frame rate differences for more info.
[edit] The Camera
A Film chain usually used a video camera tube has this reduced flicker. vidicon image pick up tube were the preferred pick up for Film chains as these gave the least amount of flicker. When CCD-charge-coupled device cameras were induced, these were also used in a Film chain, this often gave a sharper picture, but with more flicker.
Early Film chains had Black and White (B&W) cameras and many were later replaced with Color. The camera could be a standard studio camera, but most often was a camera designed for the purpose of film transfer.
Originally only Print Positive film as used. Later cameras that could invert and color correct color negative film were used.
Professional video cameras made for Film chains were used for Broadcast use.
Scene by scene color correction option was add later to film chains, first by notching the edge of the film were a color change was wanted. Later machines that counted the sprocket holes were used. At the mark (notch or electronic count number) the next stored color correction would occur. See color grading for more information.
[edit] Products
- RCA was by far the largest maker of Film chains with the high end TK-26, TK-27 and TK28. RCA made both the cameras and projectors like the early TP6.
- TeleMation Inc. made B&W and Color Film chains like the TMM-203 Multiplexer and TMU-100 Uniplexers. TeleMation cameras and later Film chain camera rack were used for the pick up. These often used Bell & Howell projectors, like the B&H 379. [Bell & Howell]] later purchased Telemation.
