To focus using autofocus with manual override (m/a): slide the lens focus-mode switch to m/a. If desired, autofocus can be over-ridden by rotating the lens focus ring while the shutter-release button is pressed halfway (or, if the camera is equipped with an af-on button, while the af-on button is pressed). To refocus using autofocus, press the shutter-release button halfway or press the af-on button again. The fast maximum aperture of f/1.8 performs brilliantly under any lighting conditions and delivers beautiful, natural background blur that brings out the best in any subject. Compatible format(s) - fx, dx, fx in dx crop mode, 35mm film