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19.1 Introduction
This chapter outlines the design steps for several photo objectives in an evolutionary way. Beginning with a single element, the Höegh meniscus, we progress by adding elements. Two elements lead to the Hypergon, a symmetrically arranged doublet. In the next step, the two lenses are shaped into cemented achromats. Finally, these cemented achromats are split into airspaced achromats, which leads to an arrangement referred to as a double anastigmat. In the final optimization, we break the symmetry and change the radii of the second achromat. The configuration is an excellent general-purpose lens with a relative wide angle coverage.
19.2 Höegh Meniscus
Emil von Höegh reasoned that if both radii of a meniscus are equal, the Petzval curvature must be zero. Furthermore, if the stop is placed at the proper position, astigmatism can be eliminated. This arrangement is shown in Figure 19.1.
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