ABSTRACT

A wide-angle lens is one whose effective focal length is significantly less than the diagonal of the format in use, with cine and video being exceptions. Consequently, by the geometry of image formation, a greater field angle of view (FOV) is obtained at infinity focus than with a standard lens. The term ‘short focus’ may conveniently be taken to indicate wide-angle lenses whose construction gives a short back focal distance, as distinct from retrofocus wide-angle lenses. For large-format cameras, the wide-angle lenses must also have some extra covering power so that lens displacement camera movements can be used. A primary application for wide-angle lenses is for architectural photography, and apart from covering power, an absence of curvilinear distortion is desirable. The large FOV of a wide-angle lens can encourage a very close viewpoint to a subject, so while including the subject very ‘steep’ perspective is given, often considered erroneously to be another wide-angle lens distortion.