This review shows performance of Canon's compact macro when used as a regular 50 mm lens.
I used Canon EOS 1Ds mark III.
Images are sharp from corner to corner starting from f/8.0.
In my opinion 50/2.5 at f/8.0 is probably the sharpest lens from Canon's EF range.
F/5.6 is not bad although we can see little softness not only in the corners but also in the edges.
At f/2.5 softness of the edges is very visible.
When I use this lens in the studio shooting full body shots I have to close it to f/8.0 or at least to f/5.6.
Contrast is very high through all the f/stops.
In my opinion this lens performs best in macro range unless stopped down.