Lastly, illumination can also affect the how accurate your auto-focus will be. This related to how much light are there in the room you are taking photo, or the setting of the scene.
For example, if the room is just too dim, the camera may not be able to sense the object you want to focus on by itself. In this case, auto-focus will not work and you need to do it by yourself.
The illumination can also affect the exposure and the speed sensitivity (ISO), which will also affect the accuracy of auto-focus.
In some cases, you will just need to do focusing yourself.