iPhone 4 detect distance using camera's focusing mechanism

Question

If I remember correctly, modern cameras send out an ultrasound wave and measure time that it takes for it to bounce back in order to estimate the focusing distance. Kinda like bats. Does iPhone's back facing camera work the same way? If so, is there any way to tap into this to detect distance and/or motion using this focusing mechanism?

Answer 1

No cameras (neither iPhone nor "real" cameras) measure the distance. They adjust the lens until it the picture is sharp. The are no ultrasound or other fancy active stuff used. So sorry there is no relaible distance info to get.