I've never used this lens, but I do have the Zeiss Makro-Planar 100 f/2 and Distagon 25 f/2, and I love those two lenses! Not only do they produce great images with fantastic micro-contrast and sharp detail when you nail focus, but their manual focus ring has a very precise feel and butter smooth rotation that makes them a pleasure to use. They have a solid heft and quality feel that lets you know they're built to last forever.
The Zeiss 135 f/2 APO Sonnar is touted as being even better optically than the Makro Planar 100 f/2, which blows my mind. I've never read a single negative comment about this lens except for the price tag and the fact it's MF only. Every quantitative test I've seen on this lens has pretty much confirmed its optical excellence. Based on available evidence, Zeiss's reputation, user reports, the photos I've seen taken with the lens, and my own experience with Zeiss lenses, I have no reason to doubt the claim that the 135 Sonnar is one of, if not THE best lens of its focal length available.
I couldn't have said it better. Pretty much spot on.

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