I ran some tests comparing my Panasonic 12-35 zoom to a Takumar f1.4/50mm and a Hexanon f1.8/40. I know that the Panasonic is quite a bit shorter than the other two, but I wanted to see if there was any significant low light advantage to the two faster, manual lenses. The results are pretty much as you would expect: The Panasonic is tack sharp, wide open at f2.8. The Hexanon f1.8/40 wide open is quite soft but it sharpens up nicely at f2.8. Likewise, the Takumar f1.4/50 is soft wide open but is quite sharp at f2.0. This give it a one stop advantage for roughly equivalent sharpness. Of course, the Panasonic lens has stabilization, so it probably can out perform the other two if mounted on a Panasonic body with no IBS. The attached photos were taken on a tripod with manual focus on the oak trunk in the center. The images were shot in RAW with no sharpening or contrast enhancement added.