ABSTRACT
Very-wide-angle lenses have fields of view greater than 100° and are of the inverted telephoto design. Such large field angles result in very large distortion—so large that a designer really should not even quote distortion as such. The lens, of course, has focal length, but has little meaning considering the large distortion. According to the cos4 law of illumination (Reiss 1945, 1948; Ray 1997), the illumination of optical systems is given by E = k cos4 θ. However, this assumes no distortion and a constant entrance-pupil diameter with field angle. Therefore, lenses obeying this “law” would have no illumination past semi-field angles of 90°.
