Television camera

(electronics) The pickup unit used to convert a scene into corresponding electric signals; optical lenses focus the scene to be televised on the photosensitive surface of a camera tube, and the tube breaks down the visual image into small picture elements and converts the light intensity of each element in turn into a corresponding electric signal. Also known as camera.

An electrooptical system used to pick up and convert a visual image or scene into an electrical signal called video. The video may be transmitted by cable or wireless means to a suitable receiver or monitor some distance from the actual scene. It may also be recorded on a video tape recorder for playback at a later time.

A television camera may fall within one of several categories: studio (see illustration), telecine, or portable. It may also be one of several highly specialized cameras used for remote viewing of inaccessible places, such as the ocean bottom or the interior of nuclear power reactors. The camera may be capable of producing color or monochrome (black and white) pictures. Most modern cameras are entirely solid-state, including the light-sensitive element, which is composed of semiconductors called charge-coupled devices (CCDs). Inexpensive or special-purpose cameras, however, may use one or more vacuum tubes, called vidicon, with a light-sensitive surface in lieu of the charge-coupled devices. See also Charge-coupled devices.

Television studio camera. (Thomson Multimedia)

Every camera shares certain essential elements: an optical system, one or more picture pickup devices, preamplifiers, scanning circuits, blanking and synchronizing circuits, video processing circuits, and control circuits. Color cameras also include some kind of color-encoding circuit.

Other functions that are necessary to obtain high-quality pictures include gamma correction, aperture correction, registration, and color balance. Gamma correction is required because the pickup devices do not respond linearly to increasing light levels. It allows the camera to capture detail in the dark areas of high-contrast scenes, essentially by “stretching” the video levels in those areas. Aperture correction provides several benefits mainly related to an even overall response to scenes with more or less detail. It also helps to improve the signal-to-noise ratio of the camera's output video. Registration must be adjusted on multiple-tube cameras to ensure that the separate red, blue, and green images are precisely aligned on one another; charge-coupled-device cameras are usually registered once, at the factory. Color balance must be properly set on color cameras and must be consistent from dark scenes to bright scenes, or there will be an objectionable tint to the camera output.

Studio cameras are equipped with several ancillary systems to enhance their operation. An electronic viewfinder (actually a small television monitor) shows the camera operator what the camera is seeing, making it possible to frame and focus the picture. The tally system consists of one or more red lights that illuminate when the camera's picture is “on the line” so that production and on-camera personnel know which camera is active. Generally an intercom system is built into the camera so that the director can communicate with the camera operator. The camera itself may be mounted upon a tripod, but more often it is on a dolly and pedestal, which allows the camera to be moved around on the studio floor and raised or lowered as desired. A pan head permits the camera to be rotated to the left or right and furnishes the actual mounting plate for the camera. The lens zoom and focus controls are mounted on a panning handle convenient to the operator.

Telecine cameras are used in conjunction with film or slide projectors to televise motion pictures and still images. Many of the usual controls are automatic so as to require less operator attention.

Portable cameras usually combine all of the basic elements into one package and may be used for a multitude of purposes. They have found their way into electronic news gathering for broadcast television, and into electronic field production, where they can be used for production of broadcast programs, commercials, and educational programs. The units often have built-in microphones, videocassette recorders, and batteries for completely self-contained operation.

Cameras used in high-definition television (HDTV) are fundamentally similar in appearance and operation to previous cameras. In fact, some modern cameras are switchable to produce either a conventional output or an HDTV output. The conventional output has a 4:3 aspect ratio raster and the scan rates match the 525-horizontal-line, 59.94-Hz-vertical-field-rate NTSC standard in the United States. When switched to HDTV mode, the aspect ratio becomes 16:9 and the horizontal scan rate is usually increased to either 720 progressively scanned lines or 1080 interlace-scanned lines with a 60-Hz vertical field rate. See also Television; Television receiver; Television standards; Television studio; Television transmitter.