The function of the camera lens is to produce the best possible optical image of the scene to be televised on the camera sensor system (tube or CCD). The lens is the first stage in the production of a good quality television picture, so great care should be taken in choosing the right one; not only for its basic optical properties, i.e. focal length and maximum aperture, but also for its quality of optical performance, i.e. resolution, image contrast, etc.
The lens will be of fixed focal length or, more likely, of variable focal length—a zoom lens. The pre-occupation with lens focal length is because the angle of view of the lens and hence the size of the shot is related to its focal length.