"The 30mm ƒ/3.5 Macro offers good results for sharpness, though it doesn't get to tack-sharp results no matter how far you stop it down. Wide open at ƒ/3.5 it has a generously sharp central region, marred only by slightly soft corners; stopping down helps a little bit with these, but even by

ƒ/8 the corners aren't as sharp as the center - and central sharpness has decreased slightly at this point as well. The break-even point seems to be ƒ/5.6, where the corners are slightly tamed, and the center isn't overly affected. It's worth noting that the differences are very slight, so you probably won't notice in every day shooting, but if you're the type to peep closely at your pixels, you might notice it."