I have the 20mm and I love it, hard stop infinity is so nice and the electronic aperture control with very snappy AF confirm for manual focus to. Build quality is awesome.
Sorry, off-topic. I'm interested in the 20mm. Is its IQ better than Canon 17-40? I need an UWA for FF because I'm moving to FF next year.
yes IMO it is better still a little soft wide open but sharpens up nicely when stopped down, colour and contrast are fantastic
and its only 52mm filter thread, you know how cheap high end filters are in 52mm? not to mention how much smaller and easier they are to carry around i think my B+W 10 stop ND was about $50 and the hoya pro 1D CPL as $40 or something.
the lens is about the same size as the 40mm pancake
for landscapes its really great it also has a unique starburst style i've not seen on other lenses at narrow apertures
it makes a great street photograpy lens on a 5Dmk3 because its small and unobtrusive
you can set it to f8 and infinity focus and know everything from a couple of meters away to infinity will be in focus
so lack of AF is not a big deal IMO and for landscapes you can be more critical using live view anyway
I think image quality wise the ziess 21mm is unbeatable however its much much bigger and much more expensive too
Since i have a 16-35 II i knew around 20mm was my favourite wide angle and the size made it something that i could easily just keep with me all the time