no particular problem in focusing at f1.1
according to my tastes this lens lose most of his attraction on a digitsal cropped sensor.
I love it on my MP with bw films, but I find it very weak on color digital shots
I shooted many photos with it and nex5, but only few were good.
too much CA, sharp only in the center at f1.1, not a great bokeh advantage at f1.1 (on cropped sensor)
it gives best performances in the very low light, see the last 4 shots (as obvious 😛 )