I have realized that in unwanted cameras, unique sensors help to target automatically. Those kind of sensors associated with some surveillance cameras change in in the area of contrast, while others start using a beam associated with infra-red (IR) light, especially in low lumination. Higher standards cameras occasionally use a mixture of both models and will often have Face Priority AF where the photographic camera can 'See' some sort of face while keeping your focus only in that. Thank you for sharing your opinions on this site.