I have taken notice that in digital cameras, specialized devices help to maintain focus automatically. The sensors involving some camcorders change in in the area of contrast, while others use a beam of infra-red (IR) light, particularly in low lumination. Higher specs cameras from time to time use a combination of both methods and may have Face Priority AF where the digicam can 'See' any face and concentrate only in that. Thanks for sharing your notions on this site.