+ The smallest lens that I have
+ Mechanical and feel very good, the focus ring turns nicely muted, as it is known from the Zeiss ZF lenses. They come from the same factory yes (Cosina, Japan).
+ Optical power: not a high flyer, but okay. Even at f / 8 you can still see a significant Vignette and the D800E it weakens the edges toward reduced resolution and light CAs, if you look closely. For "normal" viewing in Web and in print but perfectly OK, Vignette and CAs can be easily removed. For the usual distortions PTLens has eg. A correction profile.
- Actually nothing. :-) Perhaps that the lens hood is an extra and is quite expensive. A Nikon HN-1 but also fits very well.
More can not be expected from this tiny really. If you want more, you should pick up the often expensive and larger Zeiss 21mm f / 2.8.