According to my sources, the Milvus 21mm f/2.8 is the same ZF.2 optical design, with improvements in flare, and with better coatings and a new housing. In fact, the whole series, aside from the 50mm and the 85mm, are just the same, aside from the coatings and housing. As for the Planars. I always liked the 50mm, just because I did not have many close-up lenses in that lens range. However, the 100mm is so uncorrected (IMO) that I never use it. In fact, I sold off the 50mm and am selling the 100mm now. So the idea of a matched set of all these lenses has no appeal to me. I am waiting for the next Otus, which I am assured is still coming.