The Role of Aspherics in Zoom Lens Design

Zoom lenses are slowly dominating the field of general purpose imaging, and for such diverse applications as office copiers and 35 mm cinematography they are now considered of equal quality to fixed focal length lenses. For some applications, such as consumer video, fixed focal length lenses now are either rare or non-existent. Until only a few years ago aspherical surfaces could be found in only a few isolated zoom lens designs, but now a large percentage of the lenses being designed for consumer video and compact 35 millimeter, use aspherical surfaces. We undertake here to describe the function these surfaces serve.