Tap-to-focus is a handy feature on the iPhone 4 and iPhone 3GS. But did you know that exposure may also be affected by where you touch the image?
Wherever you tap the on-screen preview (before taking a shot), your iPhone will assume that that is your subject. It will adjust exposure to make sure that the subject is not too bright or dark. It may not be noticeable in most cases but if you have an especially light or dark subject the effect can be dramatic.
In the first photo I tapped on the camera, which made the image very bright. This result might be helpful if you are actually trying to show some small detail on the camera, but it made the photo too bright for my taste.
In the second photo, I tapped on the tabletop near the camera. The focus remains about the same, but my iPhone adjusted the exposure to make sure the table top is not blown out. In doing so it made the overall photo darker. The subject may be a bit on the dark side, but it looks a lot more natural this way.
