Exposure and focus come first, framing second. Half-pressing the shutter release fixes the focus and exposure settings for the shot you’re about to take. Pressing it all the way captures the frame. Use this to your advantage by metering for particular conditions, by putting your subject on one of your camera’s focus positions and half pressing the shutter to lock its settings then, without releasing the button, recompose the framing to align your subjects on the one-third power positions. This way you’ll get perfect exposures every time, whatever the composition.