Hi! This is my first post here, and from browsing other posts, I can tell that I don't know much about lens design. I apologize if this is a stupid question.
A spherical lens works best if one looks through the optical center; looking at an angle through the sides of the lens will result in oblique astigmatism. For a spherical lens, the astigmatism is the same whether the eye looks left/right or up/down. As I understand, a free-form lens design can reduce this oblique astigmatism in part of the field of view, for example on the left and right.
However, from what I understand of the optics, I can't see how this could be achieved without making the astigmatism even worse somewhere else in the field of view, at the same angle from the optical center. However, I don't read this from the marketing literature, e.g. Figure 7 in the Zeiss SV whitepaper. Although, Figures 3 and 5 in this whitepaper do actually suggest that the wider view is at the expense of the up/down field of clear vision.
Do I understand this correctly?
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