Here is a user's experience from another site:
Re: Zeiss 21mm or Nikon 14-24mm
@Dave, if you keep UV's on your glass you may like to pick up the Fotodiox filter adapter and UV. I contemplated drop kicking it at first but after some use, meaning attaching/removing cycles, it gets both easier and faster with some wear in. Hold your judgment until you've had it on and off a dozen times or so. As with many lenses, after the shotgun honeymoon and tedious get to know you phase is over, with real knowledge of it's focusing behaviors, it's a strong performer through it's wide range. If you find the left or right edge softer, place it in the sky and bob's your uncle. As much as I'd like to have a full WA set of Zeiss primes, I find myself truly satisfied with the 14-24, more so now that I can filter it for sand/water, etc.
regards and good luck.
dave G in NJ