Small digital computers and automatic optical design

The photograph reproduced in Fig. 1 is an example of good optical imagery. The picture is crisp and considerable detail is resolved all over the area, even at the extreme edges and corners. Fig. 2 is a poor picture. The reasons are obvious. While the central region is still sharp and full of detail, the rest of the area is fuzzy and ill-defined. The quality definitely deteriorates as we move further and further out from the center. These two photographs were taken with the same camera, at the same exposure, under the same subject conditions with two different lenses of the same focal length. Fig. 3 shows the lenses in schematic form, essentially a section through the lens along the axis. The poor picture was taken with the upper lens, a simple biconvex element. The good picture was taken with the lower lens, a very-well-known design called a Tessar, containing four elements, two of which are cemented together. The difference between the two pictures shown obviously is related to the difference between the two lenses which took them. The techniques which lead us from poor picture to good picture, from simple biconvex lens to multielement Tessar, form the province of optical lens design.