Focus adjusts the view and center of rotation based on displayed atoms, bonds, ribbon segments, and/or surfaces. Items that are invisible only because they fall outside the window boundaries or are clipped are still considered displayed. Any combination of atoms and surface pieces can be specified, but only those which are also displayed will be considered.
Focus with an atom-spec:
An exception to the above is that the center of rotation method is not changed if it is independent.
The center of rotation can also be controlled with the Rotation tool.
See also: center, cofr, window, the Actions menu