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Manual focus Sonnar 100/3.5 is one of the best lens ever made by any company! And it is very compact! I even seems to need no lens shade...
Who prefers a slightly shorter FL may go to the 85mm f/2.8, which has identical optical design, just compressed to 85%. It is nearly as perfect, and spectacular compactness (hardly longer than a 50mm Planar).
I have the S100 and Planar 100/2. Both are optically excellent (in different ways). The Sonnar is much cheaper and lighter, so I carry it everywhere. The Planar is awesome wide open, but really wants a heavier body like the RTSIII.
never checked it side by side with other production zeiss/contax lenses, but have h'blad, bronica, and canon systems and it is among the best performs across the board and my preferred lens on my 167, have had it a number of years with n problems or issues.
i concur re it being nearly flare proof. did not come with a hood and after initial testing i never bothered to get one.