I've had this lens for about four years. Although I don't use it often, it's a great buy at the present price (paid the equivalent of US$500 in Sep 2000 in Berlin). The lens is small, well built and optically as good or better as can be expected of a lens of this focal length, which is to say that it has sone severe light fall-off towards the corners and that it's sharp (about 40lpp/mm) in the field, degrading outside of a 18mm circle. As I shoot only negs, I cannot comment on color temp. Expect some color fringing (chromatic aberration) in the outside of a 12mm circle but not noticeable unless you enlarge over 16X.
The images I have don't really show its shortcommings, but rather its advantages. You can check some at
. PS, most lenses will mount slightly crooked, specially if used with a bayonet adapter. This does not appear to cause any vignetting with the notched integral lenshood. However, if this disturbs you, it's easily corrected by removing the rear plate and the brass shim underneath, then repositioning the thread to one of the avilable five positions. I hope this helps.