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Uh, the Canon MF's just fine - again, you might feel that the Zeiss "buttery smooth long throw" MF will provide some significant advantage - and since neither of us has used it, I suppose all we can do is speculate - but the idea that the Canon 135 poses any real problems when AF'ing sort of amuses me. ;-)
Seems to me that you'll have the same ability to "control the focal plane" with either lens.
Here's what we think we know so far:
1. Both lenses will be among the sharpest lenses available.
2. Both go to f/2
3. One can be AF'ed and the other cannot.
4. One achieves higher MFT50 resolution values on the test bench at f/2
5. One costs less than $1000 and one costs more than $2000.
The "better" idea is perhaps true, but it might be sort like telling me that $100,000,001 is better than $100,000,000. Can't argue with that. However, both amounts are huge and the difference isn't more than background noise. And if you already had $100,000,000, how much effort/cost would it be worth to you to get that extra dollar of betterness?\
Some of you probably would do anything to get that extra dollar, but many would also think that the having $100,000,000 is more or less the same.
Back to practical matters, we might be able to agree that if you often manually focus at f/2 while shooting from the tripod and then make extremely large prints of your f/2 shots you might be able to demonstrate, probably with the help of side by side comparisons and a strong magnifying lens, that your f/2 Zeiss shot is, indeed, sharper than the f/2 Canon 135 shot.
An interesting question to consider: If you would consider the Zeiss lens, would you consider buying it if the mtf50 spec at f/2 was identical to that of the Canon at f/2? If so, why? If not, what specific increment of better MTF50 resolution at f/2 do you think would be significant? If the difference at f/2 were only 10% of the difference measured in this case, would you still buy the Zeiss over the Canon? What if the difference were 1%? Would you buy the Zeiss if Canon measured 10% better? For the "buttery long throw MF" or something else?
For certain types of photography (E.g. product, fine art, portrait (some types), landscape, movies etc), what is more important than AF is the ability to precisely control the focal plane.
The buttery smooth long throw mf of the Zeiss would be better than the Canon implementation for many such applications.
Despite lack of AF, these lenses are very versatile.