Hi I am about to shoot a charity calender for a class at school and in each month there will be between 3 and 6 children. I usually use my 50mm or 85mm for portrait shots and love the wide aperture look but when I am shooting more than 2 kids how do you still get the sharp focus blur background look, is it better to use a different lens? in past experiences it is really touch and go to get a shot of say all 4 subjects in focus. Should I adjust something else on my camera. sorry for simple question!