There is no denying that Nokia produces some of the best camera phones on the market and two of these remain the 808 PureView and, more recently, the Lumia 1020. If you want to see how some camera samples from these phones compare to the Xperia Z2 then check out the 100% crops below. It shows how well the Z2 fares against these phones, although it is worth noting that the 808 PureView pictures were not taken at 8MP in oversampling mode, which probably would have produced better results. If you want to see the full samples hit the source links.
Nokia 808 PureView (top) versus Lumia 1020 (middle) versus Xperia Z2 (bottom): 100% Crops
At a distance
Nokia Lumia 1020 (top) versus Xperia Z2 (bottom): 100% Crop