In my records I found a MTF-graph, which shows resolution and contrast for the Olympus Macro 3,5/38 mm. Horizontally you see the resolution in lines per mm and vertically the contrast (%). R means the edge of the lens and M the middle of the lens. 3,5 and 5,6 are the aperture numbers. Following these graph it seems to be a good lens.
I hope that helps.