M120/2.8 is the best tele in M series from 100mm to 200mm. M150 gave a competition for the title, but otherwise I've been quite certain for a long time. This month was enough to solve that last step and now I'm ready to publish my opinion.
It's sharpest of them all. At least when comparing my copies. I don't have any test data to back up my opinion. It's based on the feeling from the shots. There's a clear step in sharpness from f2.8 to f4 and therefore I shot a lot at f4. It seems to be the sweet spot for the lens, as it combines sharpness with smooth bokeh resulting in great pop.
Bokeh is among the best in series and transition is smooth and pleasing. If extra smoothness is desired f2.8 provides clearly smoother bokeh than f4, if you are ready to let go some on the sharpness of detail. Lens also handles macro shooting well if you are ready to play with extension tubes. In real life it's often easier to change to real macro thought. Starbursts are awesome 8 pointers, thought I didn't push for nightscapes this month due to lightness. Night comes too late this time of the year. But for sunsets I rather go with M150.
There is CA. Especially wide open. But it's not the worst in series in this regard. It's nothing that stands out. Can ususally been cleared out and most of it is gone when stopped down. I've shot some pretty harsh light conditions during the month and come thru.
Build quality, handling and size are typically great. Small size makes it an easy to carry along on travels to have tele option with you just in case. It has build in hood, which is nice to have, thought I used external hood this month.
For some reason M120 is overlooked lens. Reviews in PF rate it lower than it should be. Also thought it's rare it's cheap. It goes for about same price as M100/2.8 thought stands head and shoulders above it in performance. I think this is the best value in my collection after ridiculously cheap fifties
If you're looking for one, you must look elsewhere as I'm not letting mine go in a long time. If ever.
I continue single in challenge in June with M35/2. An other great lens I've been saving to the end of the FF round.
Wide open:
f4:
f5.6:
f8:
f11: