I am using a Nikon D3200 with the stock 18-105 mm lens. I have noticed that I can't focus really precisely. If I take a picture of a structured surface at an angle, I can clearly see the limits of the depth of field, but even at its centre, the pixels are not really sharp, I can see a circle of confusion of about 5 px at the full resolution. See the image (F/5.6, ISO 100, 2s, f=66 mm, cropped):
Is that something a prime lens would solve, or a property of the chip?
>>> What makes my pixels unsharp?