[ntenny]

I have no problems with the contrast levels of my current lenses but I have not tried anything modern. I would be interested in perhaps changing lenses mid-roll. Say for instance a 1950's 50mm Sonnar with a 2012 28mm Biogon. Things like that.

It's hard to do a real-world apples-to-apples test. For instance, if you change lenses mid-roll, it's hard to separate "this lens is sharper" from "the coffee finally caught up with me and I started focussing better", or "this lens is contrastier" from "the light got contrastier". There's also that 62 years of aging on the Sonnar to think about---maybe the coatings aren't all they once were, or whatever, and the results could tell you something about old vs. new lenses but not necessarily about "classic" vs. "modern" lenses.

If you don't have problems, I think you shouldn't worry too much about the theoretical alternatives. The question is interesting, though, and I suspect careful testing would turn up some surprises.

-NT