I just got my raspberry pi yesterday and have gone through all the setup and update steps required to enable the camera extension (which took me like 6 hrs; yes, I am a newbie). 
I need to create a focus point on the camera's output and use the arrow keys to move this point around the screen. 
My question is how to access the pixel addresses in order to achieve this (if that is even how to do it). Please can one of you gurus out there point me in the right direction.
If you need to take close-ups or if you are capturing image very close to camera lens then you need to manually set the focus.
A focus point on the raspberry pi camera