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 second systems, the film projector speed is increased one frame per second to 25 frame/s. This gives a one-to-one film to video frame transfer ratio. Thus a standard two-bladed shutter can be used. See frame rate differences for more information. The camera A film chain usually used a video camera tube as this reduced flicker. Vidicon image pick up tubes were the preferred pick up for film chains as these gave the least amount of flicker. When charge-coupled device (CCD) cameras were introduced these were also used in a film chain. CCD cameras 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 professional video camera, but most often was a camera designed for the purpose of film transfer. Originally only print positive film was 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. A scene-by-scene color correction option was later added to film chains. This was first done by notching the edge of the film where a color change was wanted. Later, machines that counted the sprocket holes were used. At the mark (the notch or the electronic sprocket-count number) the next stored color correction would occur. See color grading for more information. Products RCA was by far the largest maker of film chains for broadcast with the monochrome TK-21 and the color TK-26, TK-27, TK-28, and TK-29 film pickup cameras. Its broadcast division also designed and built 16mm projectors for television use, including the TP-6, that was often used with a TP-15 Multiplexer. Early 16mm installations tended to be RCA TP-16 or Eastman 250. A different RCA division developed 35mm projectors for television use, culminating in the 35mm FR-35 and a not so well regarded 16mm FR-16 projectors. Early 35mm installations tended to be RCA TP-35. RCA's TP-66, which debuted in the early 1960s, was widely used in stations and networks for 16mm silent, optical, and magnetic sound film playback, both live on air and to videotape for editing or delayed broadcast. It is still used by a number of home