Is the Sigma 20mm f/1.4 DG HSM Art Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 20mm f/5.6 test image. Observe the contrast and resolution of these results.
Is the Sigma 20mm f/1.4 DG HSM Art Lens set to 20mm f/5.6 sharper than the Canon EF 11-24mm f/4L USM Lens set to 18mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.