ABSTRACT
The system coverage space is the region where the camera can yield a 95 per cent success rate, both in correct exposure and sharp focus. A full focusing range from infinity to a close distance is always desirable but is not always available, due to mechanical restrictions of camera or lens mount design and optical limitations. A lens forms a three-dimensional aerial image in space, corresponding to its field angle of view. The image appears visually sharp overall due to visual accommodation, but is not uniformly of good quality due to diffraction, aberration or positional effects. Various mechanical arrangements are used in a camera to provide sharp focus in appropriate photographic space. The simplest is a fixed focus lens which has no focusing mount. Mechanical focusing relies upon moving the lens axially. Alternative optical methods which depend upon altering the effective focal length of the lens need little mechanical movement.
