I'm going to use 'zooming' as meaning using the mouse scrollwheel or [-] and [+] keys to zoom in and out of one photo at a time.
Alternately, I will use 'navigating' to refer to switching from one photo to another by clicking the white quad of any photo other than the one that the viewer is currently navigated to.
Backing out from close up shots can be accomplished in at least two different ways if you started with wide angles and moved your way in to the close ups.
1: Use the down arrow key on your keyboard or the down arrow in the middle of the viewer navigation to back away from close shots, providing that there is a wide angle shot behind the current photo.
2: If you simply want to get back to wider angles which you have visited just prior to the current close up, you can use the [Z] key or the back icon on the far left of the viewer navigation icons to step backwards through your inward path.