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25mm suits me better. And 67mm filter thread is a plus. But rendering quality, micro contrast etc how do they compare to the magic 21 zf?
I prefer the angle of view of the ZF 25/2.8 (actually, it is closer to 26mm than 25mm). This fits me best for general wide angle photos. Wider than that, I prefer TSE lenses from Canon in 17 and 24, and wider still, the Samyang 14.
There is a trade off in the tolerable aberrations between the 21 (I owned the ZE version and got rid of it) and the 25.
The greatest irritation to me with the 21 is the terrible and intense vignetting and resulting central hot spot, even stopped down to shooting apertures. This was exceptionally hard to deal with for many landscapes, and particularly architecture. This lens has higher contrast than the 25, but I find the 25 to have more pleasing contrast for outdoor work.
The ZF 25/2.8 (never used the newer, better 25/2 ZF.2) has some CA to deal with, but this is not intense, reduces with smaller apertures, and is easy to clean up in PP. It is also smaller, lighter and using smaller 58mm filters.
Given the choice, my #1 pick is the older ZF version, next would be the newer heavier f/2 ZF.2 version, and lastly, I'd burden myself with the 21/2.8 model. Since you seem to be considering the 25/2 ZF.2 with its 67mm filter, I'd say go with your gut on this.
All are great lenses. Just pick your weight and price preferences! (For $500, a used ZF 25/2.8 is hard to beat! )