At the focussed distance, the image is excellent. But the depth of field only covers 2cm.
Depth of field is enhanced, but still does not cover the whole keyboard.
The image quality within the DOF has significantly lost.
Image quality is excellent along the whole keyboard. The small DOF ensures that the background influences image composition minimal.
3D focal plane alignment allows to focus on objects in different depth.
The image has been taken with f5.6.
Resulting DOF at this aperture and distance is less than 4cm.
Closing the aperture does not solve the problem of focussing objects of different distance. The diffraction effect leads to a significant loss of resolution. This influence of diffraction is an optical rule. No lens, independent of their price, can reduce this effect.
Closing the aperture by two f-stops reduces the optical resolution by factor 2. This means, that a digital back with 1/4 pixel count would result in exactly the same image quality.
In other words: A 80MPx back used at f16 will deliver the same details as a 20MPx sensor.