Quote: One of the adjustments we made in response to the test shooting results was to control the level of spherical aberration. In dose-range photography using open and larger apertures, spherical aberration was intentionally increased by a considerable level to produce a soft-focused image in which the in-focus plane in the image field appeared to be rather vague and indiscernible. ff the adjustment became too excessive, however, the image would appear completely blurred. To avoid this problem, we adjusted the level of spherical aberration bit by bit in test shootings until we discovered the optimum level, one that assured the imaging characteristics dose to our imaging goals. The final decision was made by the Limited Committee following its sensibility evaluations.
However, the lens wasn't designed to produce soft-focused images at all aperture settings. Anticipating that photographers might also prefer to close the aperture down in scenic photography, we designed the lens to produce rather crisp-focused images when the aperture is closed down to F4 or smaller.
The second paragraph suggests the lens is soft wide open...
The first paragraph explains the trade off. smooth bokeh or razor sharp images and that a compromise was made between absolute sharpness and a smooth background. What is not clear is how much softness was created to produce superior bokeh, clearly a bit of softness was introduced, but whether or not that would be soft by any other standard is open to speculation.
For those of us interested in overall rendering absolute sharpness is not a defining characteristic. For close up photography, clean smooth bokeh is worth a lot more than absolute sharpness. In fact, I can think of very few images where absolute sharpness is even pleasing. Which is reinforced by how little I like the rendering of those super sharp Zeiss lenses with their high resolution but less than optimum rendering.
I've always liked the rendering of the 31 and how it compares to any lens I've seen it compared to, and it's in a similar class. Great bokeh wide open, for flowers and close ups, (because in extreme close-ups at wide apertures is where you are most likely to encounter wonky bokeh...) and then sharp edge to edge ƒ/4 and beyond for landscapes. To me it's the ultimate design for nature. It's like two lenses in one. Too bad they're so expensive.
But since I have 14mm and 24mm covered, I may have to make an effort to acquire one. It would kind of complete the set.