In the interests of continuing my exploration of the M-P's ability to use adapted lenses, once I found my Rayqual Nikon F to Leica M mount adapter, I decided to test the Nikkor 18mm f/3.5 AI-S.
Please excuse the old git of a model ...
It was a bit of a field of view check too. Dang, 18mm is wide! The focus point was the front element of the lens ... about 22" away! I used f/5.6 to get a bit more DoF. What looks like color shifting was really a bunch of different indirect light sources, the exposure was made at around 11pm so there were flourescents, LEDs, etc all mixed together. I'm impressed with the small amount of corner darkening (and I added a bit of vignetting in LR!).
Comparing this lens to the Elmarit-R 19mm v1, the Leica lens is sharper to the corners and overall, but has much more severe light falloff. The Nikkor is on par sharp in the center but corners are a bit mushy until you get to about f/8 or so. They never quite get to the same crispness that the Elmarit-R does.
Fun to have these options ... and with a Leica M body. :-)