Hard to tell. According to some internet sources, including this one :
https://diglloyd.com/prem/s/ZF/publish/50f2Milvus.html?dglyPT=true it is the same optical design. The housing is quite different (and I do not like the new "style").
The Milvus has a gasket at the rear mount, and a very big lens shade which I never use. The front lens is recessed enough.
The main, massive differences are:
- better coatings. The ZF2 definitely has a "warm" / yellowish cast. The Milvus is pretty neutral.
- much reduced flare on stopping down. This was my only big issue with the predecessor, and I published a thread about that: shooting against the light (my usual case: pipe organs next to a big bright window) gave good results at f/2, but flare increased on stopping down. Not sure about the issue and the way it was solved, but reflections on the diaphragm blades may have been an issue.
In an issue of a German magazine (FotoRevue) with an article on macro lenses, both were analyzed, and the ZF2 was ranked sharper, while others come to opposite conclusions: sample variation? DxO also indicates some differences, esp. sharpness and vignetting wide open, rather in favour of the new version.
Bokeh-wise, they look the same, i.e. excellent. Also, LoCA is negligible, quite important for my taste.
In any case, whatever the version, this is my best "50", one stop ahead of all others in terms of sharpness. The Summicron-R and Noct Nikkor offer some magic of their own, but do not perform quite as well at f/2, and their coatings are not at the same level.
