I've been hoping something like this would pop up in the app store, but I've been watching and haven't seen anything yet. It seems like a great idea to me. Maybe it exists, and I just haven't been able to find it. The iPhone is the perfect venue for a follow focus effect. Tap one area of the screen and record.... Then tap another area and the focus shifts to that area. This already works, and it works almost perfectly. The problem that exists now is that the exposure will re-adjust for the second shot if the lighting is different than the first. That turns a great follow focus into an awkward video. Does anyone know of an app that will lock exposure, yet still allow you to adjust the focus during the shot? Thanks.