How to manually set the focus area in Android?

I created a small Android application for Android. Now I would like to know how I can tell my application (or better say the camera) that it should focus on the upper left corner of my preview.

How can i do this? What methods can be used to set focus in the upper left corner? From the documentation I know, there is a method setFocusAreas(). But I do not feel that this is very useful for my problem.

Any ideas?