Central sharpness is just fair at f/2.8, but very good by f/4 and excellent from f/5.6 to f/16. It remains very good at f/22, so having that smallest aperture is a viable and useful choice.

Central sharpness is very good at f/2.8 and f/4, excellent at f/5.6 and f/8, very good at f/11. It is still good at f/16 and f/22, but diffraction has taken hold and takes the edge off the crispness.