As I was wandering through our own lovely B&S, I happened to happen on an ad for a Nikkor 18mm AFD... And so in a moment of weakness, I bought it. :facesmack:
Ken R gaves it a sort of "meh..." review in his dedicated review for it. But then puts it on his "Nikkors to own" list a few years later? (
) He also runs it in his 17/18 ultrawide comparisons against 5 other lenses, and to my eyes, it fared pretty well.
Anyway, in a very informal, quick test, it did okay: surprisingly sharp in the central ⅔ image area, even wide open; edges and corners show a gradual softness that doesn't clean up much as I stop down. BUT, the lens has pretty severe curvature, to the point the close foreground corners become surprisingly usable, which actually can be a boon in ultra-wide landscape images.
So for right now, about all I can say is 1) it is a somewhat unique lens and 2) I like the focal length a lot -- moreso than 20. How well it performs for my actual uses remains to be seen...
PS: Another upside, is cropping to 20 eliminates a significant amount of the problem region.