Design of Aplanatic Objectives
It has already been mentioned that Abbe used the term aplanatic to refer to a lens system corrected for both spherical aberration and OSC. We shall use the term aplanat for a relatively thin spherically corrected achromat that is also corrected for OSC and thus satisfies the Abbe sine condition. As we have seen, a cemented doublet has three degrees of freedom, which are typically used to maintain the focal length and control the spherical and chromatic aberrations. To include the OSC correction requires an additional degree of freedom, which can be obtained in various ways. The principal types of aplanat will now be considered.
10.1 BROKEN-CONTACT TYPE
In this type of aplanat the powers of the two lens elements ...
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