I have observed that in video cameras, extraordinary receptors help to target automatically. The sensors associated with some camcorders change in in the area of contrast, while others work with a beam with infra-red (IR) light, specifically in low lighting. Higher specs cameras sometimes use a combination of both methods and might have Face Priority AF where the photographic camera can 'See' a new face as you concentrate only on that. Thank you for sharing your notions on this site.