I’ve touched on this briefly a couple of times, but it bears a little bit more discussion.
Bulb mode is kind of a special manual mode on your camera. On some cameras there’s a B mode on the exposure mode dial, but on others bulb is just a shutter speed– set the camera to M mode, change the shutter speed to 30 seconds (not 1/30, but half-a-minute 30 seconds) then go one step further. Once you’re there, set the aperture that you want to use.
Now what? Press the shutter button, and the shutter opens. Let go and it closes. You can keep the shutter open for as long as you want to, until your finger gets tired or your camera runs out of battery.
In order to make effective use of bulb mode, you really need another piece of hardware– a remote shutter release of some sort. I’m pretty sure that there are wired shutter releases available for all dSLRs and probably all film models too. In the simplest version, you plug the cable into the side of the camera, and when you press the button on the cable it activates the shutter. (This works in all camera modes, not just bulb.) In bulb mode, holding the button down holds the shutter open. Slightly fancier models have a shutter lock so that you can activate the shutter and then walk away for a while.
Many cameras also have wireless shutter releases available. These basically function the same way, except that they sometimes have two-press operation– press the button once to open the shutter. Press it a second time to close it. If you have a Canon Digital Rebel (original, XT, or XTi) the Canon RC-1 is a valuable addition to your kit. It lives on your camera strap and is completely unobtrusive when you don’t need it. If you want to release the shutter remotely, you just pop the RC-1 off of the strap and it’s ready to go. When you’re done, pop it back onto the strap and it’s out of your way. It’s not just for long exposures– it’s valuable whenever you want to be away from the camera, such as when you want to be in the photo. When I used a Rebel XT all the time, I was always reaching for the RC-1.
Some cameras may require you use the self-timer setting in order to use a remote shutter release. Consult your manual for the details of your specific model.
Why would you want to use bulb mode? Mostly it’s for very-long exposures of over 30 seconds, but it has other uses too. I use bulb mode a lot when I’m shooting fireworks– I try to open the shutter just as a rocket is going up, and close it as the explosion fades. You can set the camera on a tripod at night and shoot the path of stars moving across the sky, or capture blurs of cars driving through the city. Though I have no first-hand experience, bulb mode is also used for taking pictures of lightning strikes. I’m sure there are plenty of creative uses that I can’t even imagine.
Another cool technique that uses bulb mode is light painting. Light painting involves taking the camera into a darkened room, opening the shutter, and then using light sources (LEDs, flashlights, whatever) to paint light onto an object or just onto the sensor itself. While it didn’t use bulb mode, the image at left was taken by opening the shutter in a dark room then moving an LED glow ball in front of the camera. As you might have guessed by now, I like playing around in front of a camera with bright objects in a dark room– you just never know what kind of cool image you might wind up with.
Bulb mode is a specialist tool, but it’s a really useful one to know about. You probably won’t need it very often, but sometimes it’s the only real choice for getting the shot you want.
Stop Shooting Auto! 
Not sure if anyone will get this or be able to answer, but I’ve got a Rebel XT, and I’m admittedly unexpericenced with it. How do I get it into “bulb mode”? (We’ve received some huge electrical storms, and I’ve read here it’s good for lightning strikes).
Any help would be appreciated.
~Chris
I just pulled out my XT to doublecheck.
Put the camera in manual mode.
Turn the shutter speed dial (it’s the one right behind the shutter button) until you get past all of the really slow stuff (1″, 2″, etc.) The very last shutter speed, past 30 seconds, is bulb
pretty useful!
thanks a lot
I have a question,
when 2 DSLR, exactly the same model. Both Aperture set to f/22, ISO 100 and exposure compensation 0. The only different will be the 1st DSLR set to shutter 30″ while the other one set to BULB. Now shutter opened to take exactly the same scene, and the 2nd camera will be released when it reach 30″. This meant, the shutter for both DSLR are set to 30″ which the 1st DSLR set in camera shutter and the 2nd DSLR set to 30″ while in BULB mode.
Will the result exactly the same?…
Or will BULB mode more sensitive to light compared to timed shutter?
An excellent question!
The images will be exactly the same, provided they are shooting exactly the same scene. Bulb mode just means that you as a human are responsible for being the timer, rather than having the camera’s timer do it. There’s no difference between you holding the shutter open for exactly 30 seconds and the camera holding the shutter open for exactly 30 seconds.
In practice, a human will never be quite as precise as the camera. However, it’s also true that you won’t see much difference between a 30-second exposure and a 32-second exposure, except in very strange cases.
By the way, exposure compensation won’t matter in manual/bulb mode. Exposure compensation only works when the camera is choosing shutter speed, aperture, or ISO.
Thanks a lot for your prompt reply….i really appreciate it. Do comment my pic gallery on flicker if you got time…thanks alot.
So I was wondering, do I have to worry about the battery of my Minolta x-370 dying during several hour shots? I’d much rather not go miles to escape light pollution just to find my camera isn’t suitable.
I’m not specifically familiar with the X-370, so I can’t answer your question. The best thing that I can recommend is that you set it up at home and try it. You don’t even need film, or to take the lens cap off– just set up a couple of long shots and see how the battery holds out.
I’m pretty sure that the X-370 doesn’t work without a battery, though. Some old SLRs are completely mechanical, and the only thing the battery is for is powering the meter.
Yeah that is a good idea. Thanks so much for your tips and quick reply, even years later. I’ll give that a shot! Hoping to be able to get some good star trails in.
Good luck! If you do, share some with us.