Hi everyone. Thanks for this thread and the crops.
I picked up the new 28 Summicron a couple weeks ago, however unfortunately I didn't seem to luck out with a copy that was an improvement over my old Cron. For the full details, I posted my findings over at
LUF in this thread.
There were a number of aspects where the new Cron was an improvement - contrast, resistance to veiling flare, central sharpness, ergonomics, hood. But I noticed very strong forward field curvature in my copy and that image edges of planar subjects filling the frame never reached comparable sharpness to the center. My old Cron did and exceeded the sharpness of the new Cron at the edges by f/4-5.6.
I don't want to state that my new Cron was typical of how the redesign performs. Rather, that anyone buying this lens should thoroughly test it to ensure it meets their expectations and requirements.
I ended up returning it rather than trying to convince a skeptical dealer that there was a real problem with it in exchange for another one (it was the second copy I received from them after the first was clearly DOA), or have them send it to Leica for months with the possibility it would come back as 'in spec'. There just weren't enough full-rez, full frame samples available online to determine whether or how far mine was off from optimal performance.
I've since found a good used copy of the 28 Lux. There are times when I need the extra stop but the tradeoff is definitely a much larger, heavier, costlier lens. However, in the tests I've run so far, it compares favorably to the old Cron in many of the parameters I look for in images...