Written by Richard D.
Introduced in 1977, along with the AI 1.4, the 50mm f2 ai was only available for a short time but marked the start of the AI era and due to it's relative low cost sold in large numbers. Optically it was essentially unchanged from the pre-AI version.
IMHO, it's on the short list of the best Nikon lenses ever, along with the Gauss version of the 105mm f2.5 and the 180mm f2.8 ED.
I have Nikkor 50mm f2.0 AI -"K" version from midle 70's wich I converted to, so that I can use it with f90x and F70.
The front element is deeply recessed making the lens fairly flare resistant even with the relatively simple multi-coating. Widely regarded as one of Nikon's sharpest lenses, I've compared it with f1.8 and f1.4 versions and at f2 it is the sharpest of the three, giving very good sharpness wide open and superb sharpness at f5.6 and beyond, although on my D200 I've found at minimum aperture (f16) diffraction sometimes softens the image slightly. Colour rendition is typical Nikkor, with strong bright, but not unnatural colours. Contrast is fairly high, bokeh is okay but nothing special. It works well with a reversing ring to give about 1:2 maginfication.