It´s not the same lens. Look at the MTF-curves at zeiss, and you will see they are very different.
Henrik
The newer silver barrel lens from Carl Zeiss for Hasselblad is perhaps the same except may be improved coating. But the lens design for Contax 645 mount is totally different, and rather than going to 1:4, the Contax goes to 1:1, and in my point of view of higher contrast and warmer color. I do not know there is any adapter to put Contax lens on Hasselbad, it was not leaf shutter lens, nor can it be use on EOS although there is service available to put Contax N lenses on EOS and retain its full automation, in this case, the N series makro lens is also a star performer, as the older MM/ME mount makro lens from Zeiss.
The new Zeiss makro lens for ZF/ZS ie. 50/2 and 100/2 are also excellent and may be eventually will be introduced with ZE mount. And of course, the Leica Apo-Makro-Elmarit R 100/2.8 is also a superb lens, I live it when I still shoot R system, but now with Canon, the makro lens from Canon is pretty well that I will not bother using adapter for other lens, not that Canon is superior on absolute optical performance, but as a total package, I do not see such must.
Contax 645 in all counts, a great system, and certainly the Apo-Makro-Planar is among the most used and most praised lens in the line, I use it very often since day 1 until now, as coming from 205FCC, and some 500 series Hasselblad, I do not think the makro lens for Hasselblad for those days as good as Contax, after all, it is a newer design and suppose not worse.
Regards, K