distortion. Coverage of 180 deg. or more is possible, The standard aspect
ratio, or width-to-height ratio, for television pictures is four to three.
Smooth transition from wide angle to telephoto characteristics can be
obtained from zoom lenses, which change effective focal length in response to
the actuation of a single mechanical control. A good quality zoom lens may
have a zoom ratio, or apparent magnification range of 8 to 1 or more.
LIGHTING REQUIREMENTS. Improvements in television camera sensitivities
have reached the point where lighting requirements are no longer critical for
utilitarian, as opposed to artistic, applications. Illumination which is
satisfactory for the chamber crew will generally also be sufficient for video
communications. Low-light-level cameras with automatic light compensation
are available at moderate cost.
VIDEO RECORDERS. Compact, relatively inexpensive video tape recorders
have become available from several manufacturers. Typical recorders are
portable VHS units with 6-hour programming available on a single video