This is my first Olympus camera so I am not familiar with the controls. I want to have a fixed focus point in the middle of the screen. I chose this as my home position in the Set Home menu of the AF/MF menu but when I half press the shutter button the focus indicator will generally appear at this position but not always. It may show up anywhere on the screen as though the camera is deciding what to focus on instead of me. How to fix this?