Conclusion: This 20/2.8 AI-s lens is much more sturdily and precisely built than its optically-equivalent AF cousin. You could save money and get an AF version for use on your manual focus camera if you don't mind the AF lens' sloppier mechanics.
Pros: Superb FX ultrawide, and compact, too. Nikon has never made a faster 20mm lens, and this lens is smaller and lighter than any Nikon ultrawide zoom .
Cons: I wouldn't bother with this on a DX camera . I'd use any DX lens, like the 18-55mm kit lens, instead. As a manual focus lens, I wouldn't use it for sports, kids or action since it's too hard to track focus by hand.