A video camera is a device that converts a moving image into an electrical signal that—after suitable processing—can drive a television screen to recreate the original moving image. Video cameras differ from movie cameras in that their output is a stream of information that can be recorded on a magnetic tape or other storage medium, whereas the output from a movie camera is a reel of photosensitive film that must be developed before it can be viewed.
Video versus film
One of the main advantages of video cameras over film cameras is that a video recording allows instant replay of a scene after shooting. For this reason, film production teams use video recorders attached to the viewfinders of film cameras to monitor the output of each session of filming. The results on video help them decide whether repeat filming of a scene is needed.
The video format is also better suited to modern editing processes, where sequences of images can be blended and otherwise manipulated on computer before rerecording as a master video for transmission or for screening. In traditional film editing, strips of developed film had to be physically cut and spliced together or reshot through optical-effects devices, and the range of available effects was much more limited than with video. Furthermore, video recording media can be wiped and reused numerous times, whereas film stock can be used to film only once.
Video has the disadvantage of low resolution relative to film, because the photosensitive grains in film are smaller than the elements that make up the image-detecting systems of video cameras. Thus, video recording started to develop first in the television industry, while film remained the dominant medium for cinema—the inherent graininess of a video image is finer than the resolution of a television screen but becomes apparent when shown on a large screen. The development of high-resolution video cameras, hastened by the growth of high-definition television (HDTV), is helping video gain ground as an acceptable medium for moviemaking.
Video cameras have long been a favorite for making home movies, since the format requires no costly processing and the output can be played on standard video-cassette players. In recent years, the scope for more adventurous use of video in the home has been increased by the introduction of digital video cameras, whose output can be recorded on memory cards and transferred to personal computers. At the same time, increased processing power and sophisticated editing software have made it possible for the home movie enthusiast to produce professional-looking results on home equipment.
Lens systems
As with other types of cameras, the function of the lens system of a video camera is to focus an image on a focal plane. Hence, the construction and features of lens systems for video cameras are essentially identical to those of other cameras. They include compound lenses that reduce aberrations and lens coatings that cut reflection.
The simplest video cameras have a single fixed lens with focusing and f-stop (aperture) adjustments. In some cameras, screw or bayonet mounts allow easy fitting of alternative lenses, such as wide-angle and telephoto units. Fixed-lens systems are becoming less commonplace, however, and most video cameras now come equipped with motorized zoom lenses that cater to a continuous range of focal lengths, from wide angle to telephoto. The zoom is operated by two buttons that control a motor to shift the focal length up or down between its limits. The amount of zoom is usually specified as the ratio between the maximum and minimum focal length, with a ratio of 6 × (or 6:1) being typical.
Focusing can be set manually or left to an automatic focus system that uses infrared or ultrasonic reflections from the objects in view. In either case, the zoom mechanism is designed to maintain a sharply focused image whenever the focal length changes. Lens hoods help reduce glare problems, and filter systems may be used for color correction or special effects. However, color balancing and special effects are more usually achieved by electronic processing.
