Is the Rokinon (Samyang) 24mm f/1.4 US UMC Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 24mm f/1.4 test image. Observe the contrast and resolution of these results.
Is the Rokinon (Samyang) 24mm f/1.4 US UMC Lens set to 24mm f/1.4 sharper than the Nikon 24mm f/1.4G AF-S Nikkor Lens set to 24mm f/1.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.