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The Zwicky Transient Facility (ZTF) will be a major upgrade to the 48” Schmidt Camera at Palomar Observatory, which was initially commissioned in 1948. Although the optical design for ZTF is a relatively small part of the project, system requirements placed special constraints on the optical design. This paper presents the optical design for ZTF as well as the system requirements that drove the optical design.

Front converters for the iPhone 6, from six different vendors, are examined in detail. Telephoto, wide angle, and fisheye converters are examined. System performance is measured, and the measured lens designs are presented. Great variety is found in both design type and performance; little correlation is found between performance and design type.

Folded zoom lenses offer an interesting opportunity for a review of patent literature: they are of a reasonable complexity that the designs are likely to be instructive, they offer a small range of design constraints because of the standardization of CMOS imager sizes and the mechanical constraints imposed on DSC cameras, and there is enough recent activity in awarded patents that a representative sample of contemporary designs can be collected. This paper presents a review of recent patent literature for folded zoom lenses. Zemax models were built for the designs disclosed in 67 patents. For this large set of models, the distribution of paraxial properties and lens materials is presented. For the most-common design constraints, two particularly-similar disclosed designs are compared in detail. Engineering differences between the two disclosed designs are compared to differences in patent claims directed to the disclosed designs; the patents’ claims are shown to omit, at least for these two patents, some design differences that seem important from an engineering point of view.