The Pv Button
Pressing the Pv button during viewfinder photography stops lens aperture down to the current value, allowing depth of field to be previewed as long as the button is kept pressed.
Optional flash units compatible with the Nikon Creative Lighting System (CLS) will emit a modeling flash. The modeling flash can be disabled by selecting [ ] for Custom Setting e6 [ ].
You can choose the role assigned to the Pv button. Use Custom Settings f3  and g2 [ ] in the Custom Settings menu to choose the roles played by the button during photography and filming, respectively.