Is the Canon EF 11-24mm f/4L USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 14mm f/4.5 test image. Observe the contrast and resolution of these results.
Is the Canon EF 11-24mm f/4L USM Lens set to 14mm f/4.5 sharper than the Rokinon SP 14mm f/2.4 Lens set to 14mm f/2.4? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.