- alien3333Lv 71 decade agoFavorite Answer
The "B"=BULB as already described means "Bulb" and
shutter is open as long a shutter release is held down.
Bulb mode will keep the shutter open as long as you push down the shutter button.
So, you are in complete control of the exposure ...
You can also use it when cleaning a CCD and you want to keep the shutter open.
The "Bulb" shutter speed position name comes from the early days of flashbulbs,
which were invented in 1929. Prior to flashbulbs, flash powder was used.
One would open the shutter, light off the flash powder in an elevated trough
and then close the shutter again. There was no shutter synchronization with flash.
Typically you'll just want to use a timed shutter,
because most subjects don't require shutters more than a second or so,
but the bulb has some interesting and creative uses.
For example, if you're out at night and with little light,
you can leave the shutter open for a long time and capture the motion of the stars
around the north star.
I even know one guy who left his shutter open for 9 or 10 hours,
all night outside in the pitch black,
and captured a scene entirely from the light reflected off the moon!
the above pictures show you some work of done with B(BULB) shutter.
hope all help
- lee bunLv 71 decade ago
2007-04-09 01:05:52 補充：
- 1 decade ago
B 快門即是 長時間曝光,
配合手動 / 電子 快門繩,
電子繩由電子 timer 控制.