Its jaw dropping sharp, even at F2. I knew it was something special when I was focusing it on my GH1. With most ordinary lenses the point of focus can sometimes be difficult to see, and it takes a fair amount of back and forth to find the precise point of focus. Not so with this little gem. As you approach the point of focus it just gets sharper and sharper until it snaps into focus. Its even easy to focus at smaller apertures such as f8, again the precise point of focus is easy to see. It rivals my Lumix 20mm f1.7 "pancake" for being clean wide open. I now have a second lens that I would be perfectly happy to use wide open. I've used faster lenses but only used them wide open in an emergency, because of softness and CA. No such problems with the Planar.
On the M9 it is simply sensational. Extraordinary clarity. It also has a wonderful warm colour balance. All the above shots were taken in very grey light & the colours "pop" beautifully.
Certainly those T* and Planar trademarks have significance for photographers who have ever use Contax gear. They were an indication of quality then and seemingly so now.
Its not quite as well made as a Leica lens, but then not much is. The focusing ring has a typical Zeiss feel, i.e. its a bit "rubbery" However its built like a tank, compared to most DSLR lenses.
I thought my Nikon 50mm f1.2 was the best lens I'd ever used, but now I'm not so sure. A test is called for.
I'll stop gushing now!!