Overall, this lens is very sharp stopped down from about f4. At wider apertures, from 1.8 to f2.8, it's a tad soft with loss of contrast. There is almost no vignetting on the NEX-6. Still, I am not a big fan of the bokeh from this lens. I think it's not very pleasing, to me. Your mileage may vary, of course.
All pictures below were taken with NEX-6 and Helios-103 53mm f1.8 Lens.
Bokeh @ f1.8