Especially out of focus and near the corners, bokeh can often be unpleasant due to various optical aberrations: chromatic errors, a point spread function showing as coma-like or smeared or streaked halos. The lens diaphragm also has a role to play.
Hence a useful test is to observe an out of focus specular highlights as is done here.
Specular highlight bokeh
The lens was defocused here in order to study the behavior. The vehicle was struck by late-day sunlight on its tail-lamp creating a bright specular highlight.
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Since 2007, Diglloyd Guide to Zeiss is the authoritative reference and review for all of the Zeiss ZF.2 (for Nikon) and Zeiss ZE (for Canon) DSLR lenses, including the Otus line.
It includes hundreds of pages of exclusive coverage and high resolution Retina-grade examples, in-depth analysis of sharpness and contrast, color, bokeh, vignetting, distortion, MTF, and flare, and recommendations and practical usage tips.