Refer:

1.动态演示自动对焦 http://graphics.stanford.edu/courses/cs178/applets/autofocusCD.html 2.File2 http://pages.mtu.edu/~shene/DigiCam/User-Guide/5700/AUTO-FOCUS/Auto-Focus.html 3.File3 http://dougkerr.net/Pumpkin/articles/Split_Prism.pdf