Wide open, they have some flaws, but stopped down a little, the aberrations are generally well-controlled. Here's the Canon 50mm f/1.8 STM compared with the Si

Wide open, they have some flaws, but stopped down a little, the aberrations are generally well-controlled. Here's the Canon 50mm f/1.8 STM compared with the Sigma 50mm f/1.4, both at f/4: https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=989&Camera=979&Sample=0&FLI=0&API=3&LensComp=941&CameraComp=979&SampleComp=0&FLIComp=0&APIComp=4 https://www.the-digital-picture.com/Reviews/ISO-12233-Sample... The Sigma still wins in the corners, but chromatic aberrations are largely absent for both lenses. With new photographers, I often try to get them to take a 50mm f/1.8 through its paces early in their careers. One of the key milestones in the proposed shot-list is a series of images at f/8. It is eye-opening to see an inexpensive lens deliver top-notch results on even the least-expensive cameras. Beginners are often drawn to the selective depth of field of the wide aperture primes, but to me, the greatest joy of these timeless (and lightweight) double-gauss designs is their ability to render superlative quality at their diffraction-limited apertures.