The Sigma 30mm is fairly sharp but not stellar across the frame from F2.8 thru F8. Starting with F11, the effects of diffraction start to blur the images. I have not tested vignetting but I don't see it in my test shots and it is unlikely to be an issue because the lens was made for a larger image circle. The main problem that these test shots reveal is chromatic aberration, which can reduce the positive impression of a fairly sharp lens considerably. Interestingly, chromatic aberration is not corrected even on a Panasonic body.

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