Nick, when you do portrait shots with more than one person in the pic do you set the AF point selection to auto or manual centre? Some of my shots have one face in focus and the other not. Just wondered what you did. And do you know if you can select more than one focus point on manual mode as it only lets me select one of the 9 points. Auto mode is a bit hit and miss sometimes not selecting what I want in focus.
The reason you're having probs is because you need a higher F stop. The smaller the F stop the smaller the depth of field (How far back things are in focus). A low F stop gives a very blurred background very quickly as you travel away from the point of focus backwards and forwards. A high F stop and nearly everything is in focus.
Does that make sense? Your 2nd person in the above example is out of the "Field of Focus" as it where. By upping the Fstop you increase the depth of this field and therefore bring the 2nd person into focus.
You can only select 1 focus point. On auto it is just showing which areas are in focus which is why it lights up more than one spot.
nick