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I've owned a number of Milvus lenses, ZF & ZF2 lenses, but I've never owned an Otus. Is it worth the additional costs?

Zeiss Otus:

The Otus line is Zeiss's flagship, designed to offer the absolute highest possible optical performance. These lenses are renowned for their sharpness, contrast, color rendition, and minimal optical aberrations (such as chromatic aberration and distortion). They are often compared to medium format lenses in terms of image quality, offering exceptional performance even at wide-open apertures.
The Otus lenses are designed to be virtually free of optical compromises, making them some of the best lenses available for DSLR and mirrorless cameras.

Zeiss Milvus:

The Milvus line, while still offering excellent optical quality, is designed more with versatility and practicality in mind. They provide very good sharpness, contrast, and overall image quality but with some compromises compared to the Otus line. Milvus lenses are still highly regarded and are often considered among the best lenses in their class, but they are not positioned at the extreme high-end like the Otus lenses.