It didn't take long to realize that it was fault of the adapters; most of my adapters are cheap ones, and I am using two adapters for all my Leica-R lenses on the NEX-6. The reason is that I am trying to reduce the number of adapters to buy for different systems. Since I already have the adapters for Canon for most mount, I just bought a NEX-EOS mount, and then mount the Leica-R and other lenses onto the NEX-EOS adapter. Most cheap adapters don't have the precision as the more expensive ones, but most of the time we don't notice too much of it. When stacking two adapters, the tolerance quickly fades and the errors in machining adds up. Most obvious sign is one side of image is less sharp than the other side.
I guess I am going to have to buy dedicated adapters for the NEX.
Colours! - Canon 5D Mark II & Leica-R 28mm f2.8 Emarit @ f4.5.
Rain drops - Canon 5D Mark II & Leica-R 28mm f2.8 Elmarit @ f2.8.