Conclusion: Pancake lenses cannot be perfect - the small size simply implies some compromises. However, the Samsung NX 20mm f/2.8 does a pretty good job actually. At f/2.8 you have to live with some corner softness and quite high vignetting. However, the center resolution and contrast is already very decent here. The results are very sharp when stopping down to medium aperture settings. Diffraction is a limiting factor from f/11 onward.