[davidmanze]

These series of images are mostly taken in the most difficult to handle lighting conditions and frankly look pretty bad ...... with all sorts of blue and purple fringing ...... vignetting ...... some poor focusing ........ and very strong contra back lighting ..... 
 I can't believe for a moment they are representative of the lens's overall performance .......
 
 I remember taking a series of shots in a similar situation down by a river of a friend's children playing and swimming by a tree lined river using the Pentax FA 50mm F1.4 (stopped well down) ....... the results were very much the same ..... almost unusable ...... in most other situations the lens was fine.

I have no idea what exactly that blue is. Do you?

A dud lens?

 ..... looking at the blue and other fringing, I would return it for another example ....... on the Nikon forums, so far, Nikon have had their fair share of de-centered copies ..... I struggle to imagine that is how it's supposed to be on this modern lens.