With the camera set to M mode, move the shutter speed lever until "bulb" appears (after the "30 seconds" setting) and set the aperture as desired. Focus the lens and release the shutter. The shutter will stay open as long as the shutter release button is pressed. To avoid shaking the camera, mount it on a sturdy support such as a tripod and use the optional Remote Cord or Wireless Controller to release the shutter. Elapsed exposure time (in seconds) is shown in the data panel and the viewfinder display. After 99 seconds, the counter returns to "0" and continues counting.
You may want to use bulb when photographing in total darkness, which may require longer shutter speeds than thirty seconds. You can also use it for photographing fireworks, flashes of lightning or the like against a dark sky; keeping the shutter open and closing it just after the action has occurred, controlling exactly what will be captured on film.