Is the Sigma 30mm f/1.4 DC HSM Art Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 30mm f/4.0 test image. Observe the contrast and resolution of these results.
Is the Sigma 30mm f/1.4 DC HSM Art Lens set to 30mm f/4.0 sharper than the Canon EF 28mm f/1.8 USM Lens set to 28mm f/2.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.