Maybe KEE friends have experienced that their photos are out of focus even though the autofocus on the lens has sounded, indicating that it is in focus. This is experienced by many DSLR camera users because the AF mechanism is separate so there is a chance of missing focus, which doesn't happen if you take photos in live view mode or AF with contrast detection like on a mirrorless camera.
Usually this happens when the camera is looking for focus. Without contrast detection on a DSLR camera, the camera doesn't really know whether the focus is correct even though the camera makes a focusing sound. Focus may fall slightly backward (back focus) or forward (front focus). For example, when you direct the focus point to someone's eyes, it turns out that your photo is less sharp, but instead the ears are sharp. This means that your camera is experiencing back focus.
Source : http://www.infofotografi.com/
This is mostly experienced by DSLR cameras with large apertures such as f/1.4. But there are also DSLR cameras with f/4 aperture that experience this. If you experience back focus, the solution is to avoid using the largest aperture. You can use f/5.6 or smaller. Or you can also calibrate the lens AF on your DSLR camera, known as the AF fine tune (Nikon) and AF microadjustment (Canon) features by telling the camera to shift the lens focus slightly forward or back.