quite good but not as good as I was expecting it to be 
Richard, you mention spherical aberration wide open at f/4.0. Please correct me if I'm wrong but I associate some under correction of spherical aberration with good bokeh. Nikkor - The Thousand and One Night mentions that spherical aberration is under corrected at portrait distances and wide apertures in the 105/2.5 AI (Xenotar type) and this is what makes defocused backgrounds appeared beautiful. A friend owned a 105/4.0 AI Micro-Nikkor and said it made a good portrait lens noting good bokeh at f/4.0.
How does it compare to the 105 2.8 Ais micro Nikkor?
Using the 105/2.8 AIS between 1:2 and 1:1 is complicated as this lens has CRC or floating elements. The lens should be kept at its minimum focus position and as little extension used to achieve the desired image ratio. One could use a PK-12 then PK-13 then both before using a PN-11. I wonder if anyone bothers to do this? There are suggested maximum apertures to use engraved on the barrel of the 105/2.8 AIS Micro. I believe this is for edge sharpness. It's easier to use the 105/4.0 AI or AIS and use the PN-11 to go from 1:2 to 1:1 as the 105/4.0 Micro is a unit focusing lens with no CRC.
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I bought a 105/4.0 AI Micro-Nikkor as soon as it was released but returned it. I was pretty green. I used a PK-13 tube and took photos of bees at 1:1.3 and marked f/32. The results were quite soft. I believe this is an effective f/57. Even then I probably knew better than to use f/45~f/64 with 4x5 due to diffraction. Years later I bought a friend's 105/4.0 AI Micro-Nikkor. I've only used it with a PN-11.
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My thoughts renegading the 105/2.8 AIS Micro v. 105/4.0 AI/AIS Micro are use the 105/2.8 for a general 105mm, a portrait lens and close-up to 1:2. Use the 105/4.0 AI and AIS Micro as a general 105mm lens, portrait lens and 1:2 to 1:1 and beyond.
Dave
