The 23.3 mm is the telephoto ( *tele* ) end of your zoom. The 4x is the zoom ratio using 23.2mm/5.8mm ( The longest focal length of the zoom divided by the shortest )
Shoot at the telephoto end at the widest possible aperture and have yourself move back to frame the same shot and try. Using a longer focal length can appear as though the depth of field is reduced and while having your subject in focus, having abit more blur at the background too.
Ryan
Buddy,
so you mean is, i zoom in 4X and move back to get the same size of subject.. but may get better blur effects right?