You also can choose different views by clicking the little down-pointing arrow to the right of the Before/After view button. A pop-up menu appear with a list of Before/After view choices. In Figure 3, I chose Before/After Top/Bottom. To get the biggest preview possible, I also pressed Shift-Tab to hide the right-side panels and the filmstrip.
By the way, when you’re in one of these Before/After views, zooming in and moving around one photo affects both photos at the same time. So if you zoom in on the After photo and start scrolling around, the Before photo zooms and moves right along with it. (In Figure 3, I zoomed in on the After photo, and then moved around the image by clicking-and-dragging. As you can see, the two zoom views and the zoom locations are identical.)