Tim has recently made this excellent Field Review of the Carl Zeiss Distagon 2.8/21mm ZF.
Tim Ashley Photography | Zeiss 21mm F2.8 ZF2 on D800e: Field Review, Tips 'n' Tricks
I have now bought a used sample of the 21mm, and I can only confirm Tim's findings e.g. with the field curvature.
Yesterday I tried out the Zeiss ZF in comparison to my Voigtländer Color-Skopar 3.5/20mm SLII Asph.
I think it's pretty clear that the Zeiss lens has the edge especially by being a bit more contrasty, still I'm surprised how well the Voigtländer holds up.
I wasn't really able to focus in Live View partly because of the bright sunlight reflected by the snow and partly because I got tears in my eyes due to the cold and a windy weather.
One of those occasions where I really missed autofocus.
But at f/8 and using focus bracketing I was able to get a couple of lucky shots with more or less everything within acceptable DOF, and I just picked the best shot from each lens.
This is in no way scientific, the sun was now and then breaking through some heavy clouds behind my bag and the light was quickly changing with regards to brightness as well as color.
This time I removed the lateral color aberration when processing the files, but you can download the RAW files and see for yourselves.
I also did not add the full amount of EV because with a bit more darkness I find it easier to judge sharpness, but you can just process the RAW files to your own taste.
The Voigtländer 20mm
801_3233_Voigtlander_20mm_at_f8.NEF
click for native size (6.7 Mb)
Nikon D800E • Voigtländer Color-Skopar 3.5/20mm SLII Aspherical • 1/180 sec. at f/8 ISO 100 • Lightroom 4.3
The Zeiss 21mm
801_3212_Zeiss_21mm_ZF_at_f8.NEF
click for native size (7.2 Mb)
Nikon D800E • Carl Zeiss Distagon 2.8/21mm ZF • 1/180 sec. at f/8 ISO 100 • Lightroom 4.3