Canon EOS7DBODY User Manual (en)

When bulb is set, the shutter stays open while you hold down the 
shutter button completely, and closes when you let go of the shutter 
button. This is called bulb exposure. Use bulb exposures for night 
scenes, fireworks, the heavens, and other subjects requiring long 
Set the Mode Dial to <F>.
Set the desired aperture.
While looking at the LCD panel, turn 
the <6> or <5> dial.
Take the picture.
While you hold down the shutter 
button, the exposure will continue.
The elapsed exposure time will be 
displayed on the LCD panel.
F: Bulb Exposures
Elapsed exposure time
Since bulb exposures produce more noise than usual, the image might 
look a little grainy.
When [8C.Fn II -1: Long exp. noise reduction] is set to [1: Auto] or 
[2: On], noise generated by the bulb exposure can be reduced (p.208).
For bulb exposures, using the Remote Switch RS-80N3 or Timer Remote 
Controller TC-80N3 (both sold separately) is recommended.
You can also use a remote controller (sold separately, p.110) for bulb 
exposures. When you press the remote controller’s transmit button, the 
bulb exposure will start immediately or 2 sec. later. Press the button 
again to stop the bulb exposure.