There is more incorrect information floating around concerning these lenses than correct information. The lenses which were not as good at infinity (although some consider them better at 1:10 and higher magnifications) are marked Micro Nikkor Auto. These have mechanical compensation in the close range. The first version has a silver colored (aluminum) inner barrel. the second version has a black colored inner barrel. Both have metal focusing rings with no rubber cover. The Micro Nikkor P was the first model (the first model with an auto diaphragm) to have rubber covering the focusing ring and to have the optical formula slightly changed. It and all of the remaining 55/3.5 Micro Nikkors work well at infinity. The Micro Nikkor PC had improved coating. The next model, the 'K' had similar cosmetics to the later AI. There was no AIS version of the 55/3.5 Micro Nikkor. The successor lens was the 55/2.8 Micro Nikkor AIS which had a floating element design and which is considered excellent for both near and far subjects.