Victor, I think it has everything to do with how and what you shoot.
Like you, I used a Contax 645 with both the Zeiss AF lenses including the 350/4 APO ... and a NAM-1 adapter to use my relatively vast collection of V lenses both CF and FE. It became more and more apparent that outside the studio,
I wanted/needed AF for my style of more spontaneous shooting. When it became crystal clear that the C645 would never improve the AF, I moved on to the H system ... which has continually improved the AF system, and along with it my In Focus hit ratio ... culminating with True Focus and the H4D/60 where DOF and focus accuracy is even more critical. IMO, minor differences in optical qualities pales in comparison to too many OOF shots.
Then along comes the S2 with unquestioned optics (IMO), and AF. When I tested the S2 before buying into the system, almost all the time was spent testing the AF and form factor for my style of shooting.
I also just "LOVE" getting older ... where the sins of youth visit themselves on you with a vengeance
I have a bone-on-bone arthritic sports knee that should have been totally replaced a decade ago, and I broke a couple of toes in the Studio a couple of weeks ago ... good thing I don't have a wedding to shoot soon :ROTFL: Plus when younger, I severely damaged my right eye, and it is also getting worse faster than my left eye ... making AF more important. I can focus the M even with the 0.95 because I use mags ... plus rangefinders are easier to manually focus anyway.
So, lugging around a really big system is something I'm less inclined to do now ... but I'm addicted to file quality.
The only adapter I now own is one to use Leica M lenses on a Sony NEX ... and I don't consider it a serious item, more for fun. I truly am not interested in any adapted anything and sold all of my V system and even the CF adapters to use V lenses on the H camera ... even though the H had focus confirmation with manual V lenses. It was all just too slow.
Sure I'd like to "try" a 350SA on a S2 ... but it is not something I'd ever buy ... I just do not use longer lenses very much ... actually hardly at all. I'd like to see a 1/4X APO extender for the Leica S180 and that would be all I'd ever need.
So, it is all predicated around what and how you shoot.
-Marc
Me in my "Big Zeiss Lens" days ...
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