For a while I'm thinking about buying new DA 50/1.8. I dont know if I need one - so I just done one test.
Controlled light, tripod, ISO 100, same manual exposure, manual WB and six lenses that have 50mm FL. I made comparison charts, in full resolution are available on flickr. First picture is the scene (Olympus OM at f4), second is crop near the center and third is crop near the edge. It is absolutely without post proces. Only developed from RAW in ACR (set sharpening, contrast etc to 0).
Competitors are:
Pentacon 50/1.8 MC
Adapted Olympus OM 50/1.8 MC
DA* 50-135
DA 50-200 WR
DAL 18-55
DA 18-135 WR
My observations:
Olympus 50 is clearly best at any given aperture. It can be seen in center, but near edges it is more pronounced.
Second place shares Pentacon with DA*. Star is sharper in center, but Pentacon (is FF) near edges.
From other zooms is CENTER winner 18-135 and EDGE winner is kit DAL 18-55, I think.
So if I will finally decide to buy new DA50/1.8, I hope that will be on par with Olympus or better...