Does Nikon D5200 is gonna have similar problem of fixed aperture in live view as its predecessor??
Due to the way the mirror cage/diaphragm setting mechanism works in Nikons, it is not possible for the aperture to change in the live viewing mode once the mirror goes up. Aperture is mechanically locked at that setting till the camera cycles again right before shooting the picture.
Since the physical size of the aperture is controlled by the position of the lever inside mirror opening and not electronics (i.e. Canon) it is not practical to do what you want without a completely different lens/body diaphragm control design.
|AF4_2483 Surfing the Serengeti by DaveInHouston|
from Hot Air Balloon view
|Peregrine Falcon by Psychic1|
from Best Wildlife Photo of the Week - 4