The lens on your G-III needs to be calibrated, meaning the flange-back distance needs to be reset. The 40/1.7 on the G-III is a very good lens wide-open, sharp and contrasty, but if the register is off, you get mush.
Originally Posted by David Lyga
There was a long discussion on this subject over on RFF (or the Classic Camera Repair Forum) a few years back. One of the guys experimented with changing the flange-back distance on his G-III. Once properly calibrated, the results were quite good. If you know what you are doing, you can do it yourself. Not hard if I recall, but the effort is worth it.