TELEVISION CAMERAS

Video Camera

TELEVISION CAMERAS

The television cameras are used to convert the optical information or picture into an electronic signal. This information can be stored on videotape, optical disks or computer memory. This stored electronic signal can be easily transmitted to the receiver and can be displayed on a television or monitor. Television cameras are very easier to operate rather than film or still cameras because they can watch and control the output of the camera as our choice. On the television camera, some controls are present, either these are electronic controls or the manual controls. These controls are very simple and anyone can very easily familiar with these controls.

Television Camera, Video Camera
Television Camera

Television cameras have many different physical and electrical configurations. But, in general, they can be divided into two basic groups—self-contained cameras and two-unit systems. The two-unit camera system has separate camera heads, which driven by remote camera control equipment. This remote control is situated far from the camera head. A self-contained camera can easily generate a complete television signal because it has all the necessary elements which are used to view a scene.

The remote camera head usually contains only photosensitive pick-up tubes, its associated deflection circuitry, video preamplifier, and a video monitor. Thus the bulk of the circuitry is contained in the camera control unit, which is connected to the camera head by means of a multiconductor cable. This cable not only carries video, deflection and sync signals but also feeds high voltage supplies necessary for the camera tube. The remote camera control unit contains most of the electrical operating and set-up controls. For this reason, it is usually located near a viewing monitor so that the results of any adjustments may be easily viewed on the monitor screen. All camera controls are available on a panel in the production control room.

Camera Lenses

Television cameras can produce images to different scales depending on the focal length or viewing angle of the lens which is used in a camera. Lenses of longer focal length are narrow-angle lenses while those of shorter focal length are wide-angle lenses. Those lenses have a narrow angle (below 20°) are used for capturing close up pictures of distant objects because of its magnifying effect due to their longer focal length. Those lenses have an angle over 60° that are most suited for location shots that cover large areas. Medium angle lenses (20 to 60°) are called universal lenses and are used for televising normal scenes. All lenses consist of a combination of simple lens elements to minimize spherical aberration and other optical distortions.

            The focal length is a very important term for lenses. It is the distance from the optical center of the lens to the focal plane (target or chip) of the video camera when the lens is focused at infinity. The focal length is generally measured in millimeters. In the case of lenses with fixed focal lengths, then it is like a 10 mm lens, a 20 mm lens, a 100 mm lens, etc.

Lens Turret

A judicious choice of lens can considerably improve the quality of image, depth of field and the impact which is intended to be created on the viewer. Accordingly, a number of lenses are used and these lenses have different viewing angles. Their focal lengths can be adjusted by adjusting the target element which is placed in front of the barrel of the lens assembly. This lens compliment of the TV camera is mounted on a turret. The lens turret is screwed in the front of the camera and rotation of the turret brings the desired lens in front of the camera tube. The turret of an image orthicon has four lenses with different focal lengths. These focal lengths are 35 mm, 50 mm, 150 mm. Also has a zoom lens of 40 to 400 mm such a lens turret mounted in front of a television camera.

image orthicon turret assembly
Image Orthicon Turret Assembly

Zoom Lens

A zoom lens has a focal length which varies in a range of 10: 1 or more. In this lens, the viewing angle and field view can be varied without loss of focus. This enables dramatic close-up control.

The smooth and gradual change of focal length by the cameraman while televising a scene appears to the viewer as if he is approaching or receding from the scene.

The variable focal length is obtained by moving individual lens elements of a compound lens assembly. A zoom lens can in principle simulate any fixed lens which has a focal length within the zoom range. It may, however, be noted that the zoom lens is not a fast lens. The speed of a lens is determined by the amount of light it allows to pass through it. Thus under poor lighting conditions, faster fixed focal length lenses mounted on the turret are preferred.

In many camera units, only a zoom lens is provided instead of the turret lens assembly.

This alone enables the camera operator to have close-ups, wide coverage of the scene and distant shots without loss of focus. This is particularly so in color TV cameras where the scene is often well defined and suitably illuminated for proper reproduction of color details.

Camera Mountings

The studio cameras are mounted on lightweight tripod stands with rubber wheels. So it can able to easily operate and to shift the camera as and when required. It is often necessary to be able to move the camera up and down and around its central axis to pick-up different sections of the scene. In such cases, pan-tilt units may be used which typically provide a 360° rotational capability and allow tilting action of plus or minus 90°. In many applications, the primarily closed-circuit systems are used. So it is desirable to be able to remotely move the camera both horizontally and vertically, small servo motors are provided as part of the camera mount. Small motors are also used for remote focusing of the lens unit. In exceptional cases when an overview of a scene is necessary, a remotely controlled camera is hung from the ceiling.

Studio Lightings

In a television studio, it is necessary to illuminate each area of action separately besides providing an average level of brightness over the entire scene. The lighting scheme is so designed that shadows are prevented. As many as 50 to 100 light fittings of different types are often provided in most studios. The light fixtures used include spotlights, broads and floodlights of 0.5 KW to 5 KW ratings. A number of such fittings are suspended from the top so that these can be shifted unseen by the viewer. In big studios catwalks (passages close to the ceiling) are built for ease of changing the location of the suspended light fixtures.

The brightness level in different locations of the studio is controlled by varying effective current flow through the corresponding lamps. For a smooth current control, dimmer stars (autotransformers) are used for low rating lamps are silicon controlled rectifiers (SCRs) for higher power lights. The power to all the lines is fed through automatic voltage stabilizers in order to maintain a steady voltage supply. The mains distribution boards and switches are located in a separate room close to the studios. The dimmer stars and other light control equipment is mounted on a separate panel in the program control room.

Audio Pick-up

The location and placement of microphones depending on the type of program. For panel discussions, news-reading and musical programs the microphones may be visible to the viewer and so can be put on a desk or mounted on floor stands. However, for plays and many other similar programs, the microphones must be kept out of view. For such applications, these are either hidden suitably or mounted on booms. A microphone boom is an adjustable extended rod from a stand which is mounted on a movable platform. The booms carry microphones close to the area of pick-up but keep them high enough to be out of the camera range. Boom operators manipulate boom arms for distinct sound pick-up yet keeping the microphones out of camera view.

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