I have been successfully using a Sigma 105mm, f/2,8 DG Macro on a Panasonic G1 with a DMW-MA1 adapter for some months. What adapter are you using? On my set up auto focus DOES NOT function, however auto stop down DOES function. Are you certain that your lens is both auto focusing and auto stopping down. It looks to me as though your poor shots on the m4/3 camera could be taken at maximum aperture and the lack of depth of field has caused you to assume a lack of sharpness.
Thanks Barrie. I am using the MMF2 that came with the 2 lens kit. The AF works in S-AF mode but not in the C-AF.
Guess what..I was searching through the EXIF, In broad daylight, the camera set itself to ISO500 and 1/200s It was f8 for the spider and f6.3 for the fly. Now I know why the lack of details. Should have default it to ISO 200 or 250.
P.S. Are you the same Barrie from a four third forum?
Glad you have been able to resolve your problem.
I have posted in a 4/3 forum in flickr, although I haven't visited it for some time. Otherwise there is someone else out there with the less common spelling of my name.