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Videotape Recorders
Figure  13-4.Video  scanning.

Photography (Basic) - Introduction to photography and other graphic techniques
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Figure 13-3.–Basic principles of a motion-video camera. Tape  Format  Systems The classification of a videotape recorder VTR by tape width was particularly important in the earlier days when the quality of the videotape recording was directly related to the tape format. The old standard used to be, the  wider  the  tape,  the  higher  the  quality  of  the recording. Anything smaller than the l-inch videotape was considered small format and inferior in quality. Today, 1/2-inch Betacam SP can provide equal or superior quality compared to the large-format, l-inch machines. The Hi8 video camera (8mm) is superior to the 1/2-inch VHS cameras. Today, “small format” is used mainly to describe small, highly portable television equipment,   such   as   small   camcorders.   Like   all state-of-the-art  electronic  equipment,  smaller  no  longer implies  inferior  quality. The quality of the tape itself has much to do with the quality of the picture. No matter how sophisticated the video hardware, the resulting picture is only as good as the videotape being used. Videotape  is  a  ribbon  of  polyester  film  base  coated with magnetic iron-oxide particles. The surface of the tape, or emulsion side, that faces the video recorder heads is highly polished to maximize tape-to-head contact  and  to  minimize  wear  on  the  heads. Head clogging results when oxide comes off the tape and gets caught in the head gaps of the recorder. If the tape clogs the video recording heads, you cannot play back or record. Normally, the heads will clog after recording or playing back half a dozen or so tapes. You should  have  the  heads  cleaned  according  to  the manufacturer’s  recommendations  or  according  to Planned Maintenance System (PMS) requirements. Videotape dropout occurs when a piece of magnetic oxide or coating on the tape flakes off or is rough, causing a “hole” or line of missing information in the picture when it is viewed on the monitor. Dropout appears on the TV screen as little black or white lines, darting across the picture. The main causes of dropout are dirty heads or imperfections in the tape. Once dropout occurs, it cannot be replaced or corrected on the tape. There are no black-and-white or color videotapes. Any videotape will record either black and white or color. Black and white or color depends solely on whether the camera and monitor are black and white or color. THE VIDEO CAMERA Refer to figure 13-3 to help clarify how a video camera operates. In the video camera, an image (a) is gathered by the camera lens (b), and focused on the face of  the  camera  pickup  tube  (photocathode)  or  a solid-state imaging device (c). The face or screen of the photocathode  is  covered  with  thousands  of  light sensitive dots. As light from a particular part of the scene falls  on  each  dot,  the  dot  becomes  electrically  charged. A charge pattern is built up proportionally to the brightness of the scene. An electron beam in the pickup tube emits a steady beam of electron particles. This electron  beam  scans  the  charged  pattern  on  the photocathode and reads over it in a series of lines. The scanning beam neutralizes each picture element or dot and  produces  varying  electrical  currents  (the  video signal). These currents are proportional to the charge pattern which are proportional to the light transmitted through the lens. The current or video signal (picture) is amplified (d) and then recorded on tape by rotating heads (e) and then converted  back  to  visible  screen  images  in  the viewfinder  (f). As each dot on the tube screen is scanned, the dot gives up its information and is wiped clean so the tube screen  can  respond  to  any  new  light  it  receives. 13-6







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