What's wrong with the 35 ASPH Summicron? I really want to know!!!
There is nothing wrong with the 35 Cron ASPH. It is among the best lenses Leica has ever made.
The Cron ASPH and Summilux ASPH perform pretty much identical, except of course the Lux is a stop faster.
The Cron ASPH is slightly sharper at f2 and f2.8 than the v4 pre-ASPH Cron (mostly in the corners).
The Cron ASPH has a shorter transition to out of focus than the pre-asph model, because it is more highly corrected. That said the Cron ASPH has exceptionally smooth bokeh for a ASPH design.
The Cron ASPH delivers images as flat as a pancake, which means that your test shots of your favorite brick wall will be...well, as flat as a brick wall. In other words geometric distortion is non-existent.
I have the v4 pre-asph Cron (recent Leica CLA) and a Summilux ASPH. Their performance is very similar as is their fingerprint.
As far as I am concerned the 1.4/35 Summilux ASPH is a contender as perhaps the best lens that Leica has ever made.
The balance of sharpness, contrast and glow is perfect. I don't know how they did it, but while this lens is stunningly sharp at any stop it doesn't produce images that feel brittle or harsh. It is exceptionally flare proof, yet it glows like the older Mandeler designs. I've made some 16x20 fiberprints that have such a three dimensional quality to them that they look like they are going to leap off the page. Even laymen comment on this phenomina.
But in any case you really can't go wrong with any of these three (v4 pre-ASPH Cron, Lux ASPH or Cron ASPH).
The pre-ASPH Lux is a gem in it's own right. From f4 on down it can't keep up with the other three lenses as far as sheer performance goes. At f1.4 and f2 it simply is soft. BUT MTF charts aren't everything. The pre-ASPH Lux draws pictures with the same magic that the collapsible Summicron does, so it certainly has its place.
Look here for a technical review:
http://www.imx.nl/photosite/leica/mseries/testm/m2-35.html