AllAboutSymbian has performed a comprehensive shoot-out between the Nokia 808, Lumia 1020, Samsung Galaxy S4 Zoom and the Nokia Lumia 925, where the later represents the average camera phone and the three earlier devices camera-focussed phones.
One of the results, a macro shot in good light, is above, with the Nokia 808 top left, the Nokia Lumia 1020 top right, the Samsung Galaxy S4 Zoom bottom right and the Nokia Lumia 925 bottom left.
In the above example the Nokia Lumia 1020 (top right) achieves a spectacular result,but in other tests where any zooming in was applied the Galaxy S4 Zoom did perform better than the other handsets, despite the lossless zoom of the 808 and 1020.
Overall AAS scored the phones:
It seems clear that, as one expects from camera-focussed handsets, their performance is miles ahead of regular devices such as the Nokia Lumia 925, and the large camera-like form factor of the Galaxy S4 Zoom does not provide a clear advantage over the other devices except when zooming in.
See many more camera comparisons at AllAboutSymbian here.