Quote from the respected Ken Rockwell: 

"This AI-s lens (1981-present) is completely different from the older AI lens. Nikon made a big upgrade to the optics when they upgraded it to AI-s, and they really pulled out all the stops.

Not only does this Nikkor uses 8 elements, it also uses floating elements to optimize its performance as it is focused at every distance.

This is also Nikon's closest-focusing lens, with a close-focus distance of 7 inches (0.6 ft), or 20 cm.

There is no sharper manual-focus wide angle lens made by Nikon, and it is the only Nikon wide angle, along with the 15mm f/3.5, that is completely free from barrel distortion at ordinary distances.

Optically this is an almost perfect lens, and one of the most perfect lenses you can get to fit a Nikon camera."