7ef8676a_Photo_Editing_with_Aperture__Multi_Touch_trackpad_gestures
[Feature] Loupe tool [Multi-Touch trackpad gestures] 
Use the pinch gesture to change the Loupe size. (As with previous versions of Aperture, you can also use the scroll gesture to change the Loupe magnification.)
Photo Editing with Aperture
Multi-Touch trackpad gestures