Using the additional screen space of a second display provides an excellent platform for viewing and performing image adjustments, playing slideshows, and presenting your full-color, full-size photos to clients. When your system uses two displays, Aperture provides two Viewers in which you can view multiple photos. These Viewers are called the Main Viewer and the Secondary Viewer. The Main Viewer is used for displaying the Aperture application, and the Secondary Viewer for viewing photos. You can choose whether Aperture displays the same photos in the Main Viewer and Secondary Viewer, displays only the currently selected photo in the Secondary Viewer, or splits the display of photos between the Main Viewer and the Secondary Viewer.
To display the same photos in the Main Viewer and the Secondary Viewer: Choose View > Secondary Viewer > Mirror (or press Option-M).
To display the currently selected photo in the Secondary Viewer: Choose View > Secondary Viewer > Alternate (or press Option-A).
When you choose this option, the Secondary Viewer shows only one photo, even when you have the Main Viewer set to display multiple photos.
To display a selection of photos across both the Main Viewer and the Secondary Viewer: Choose View > Secondary Viewer > Span (or press Option-S).
This option splits the display of the currently selected photos between the Main Viewer and the Secondary Viewer. For example, if you select seven photos to view, the Main Viewer shows as many as fit its screen size, and the remaining photos appear in the Secondary Viewer. Thus, one Viewer might show four photos, and the other Viewer might show the remaining three of the seven. You can also use the Span option to select two photos and compare them, showing one photo per display.
To turn off the display of photos in the Secondary Viewer, making the screen black: Choose View > Secondary Viewer > Black (or press Option-B).
This option sets the Secondary Viewer to be a blank screen.
To turn off the dual-display function: Choose View > Secondary Viewer > Off (or press Option-X).