I have observed that in unwanted cameras, unique receptors help to focus automatically. Those sensors with some digital cameras change in in the area of contrast, while others use a beam with infra-red (IR) light, specifically in low light. Higher specification cameras at times use a combination of both devices and could have Face Priority AF where the camera can 'See' some sort of face while keeping your focus only on that. Thank you for sharing your thinking on this blog site.