Better built than most of today pro lenses this little gem was one of the E Series glasses.
This series has been produced by Nikon in the ’70s to compete in the market with a bunch of low priced lenses (“E” stands for “Economical”).
Nevertheless a few of this glasses have become jewels. This 100 Ai is one of them.
It is as sharp, or often sharper, than the 70-180 Micro Nikkor, a great lens per se. But the Micro Nikkor costs 1200 USD or more, while the 100 Ai 100 USD in mint condition.
If you find one get it, except if you shoot portraits; in this case the 85/1,8 will better fit your needs because the largest maximum aperture.
Picture from Nikon.com
Exept for the ugly plastic covered barrel you don’t have a reason to not buy this lens (unless you want its big brother 85/1,4 AF).
It is biting sharp, lightweight, small, fast and cheap.
One of the Nikon legends.
Big and heavy, but beautiful.
You may obtain very crisp images from this lens, but you have to put it on a rock-solid tripod (or shoot whit a lot of light at high speeds), maybe interlocking something between the tripod mount and the lens itself to avoid vibrations (often a rollfilm plastic case filled with something is good enough).
It could be a useful travel companion, but for my tastes is too dark, so I use it mainly for landscape and macro work.
It is sharp wide open, and past two stops down don’t improve so much.