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What is the estimated battery consumption when using bulb mode for an exposure about an hour long? I know the best thing is to test it out, but I'm not in position to do that right now.

Camera is Canon EOS 20D, and lens is Sigma 14mm, if matters.

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Depends on battery life and current temperature. Do you have brand new batteries and are you operating at 72degrees F? –  dpollitt Aug 12 '11 at 17:56
    
It's also worth noting that generally the camera will generally stop the exposure, save the image file, and then shut down when the battery dies, rather then lose the image. It's a bit OT, but the only way to get a non-noise-reduced RAW file out of some Nikon cameras is to remove the battery during the exposure. This forces the camera to do as little processing as possible. Anyways, even if your battery does not last, you shouldn't lose the results of a long exposure. –  Fake Name Aug 13 '11 at 9:00
    
@Fake Name, yes you are right, my battery lasted for probably 20min, it was not fully charged, and it was pretty cold, but exposure wasn't lost :) i.min.us/idNkzYKYK.jpg (it was full moon so you couldn't see all the stars) –  webarto Aug 13 '11 at 10:30

1 Answer 1

up vote 2 down vote accepted

From the Canon Digital Learning Center:

For long exposures, camera makers rate the battery power in terms of total length of time a freshly-charged battery can hold the shutter open. Here are a few examples supplied by Canon’s engineers, at 73°F/23°C:

EOS Rebel T1i, Rebel XSi, Rebel XS: Approx. 2 hours
EOS 50D: Approx. 2.5 hours
EOS 5D Mark II: Approx. 4.5 hours

Most Canon EOS digital SLRs accept an optional Battery Grip, which does allow the photographer to install one or two rechargeable batteries. With two batteries installed, any of the above figures would be doubled. Battery grips with an extra battery pack can be a great accessory for extensive shooting of fireworks displays.

The battery that is supplied with the Canon 20D is the BP-511A, and it has 1390mAh. I believe this is the same battery that is in the EOS 50D that has the specs outlined above. To that degree, you could probably assume similar performance of approximately 2.5hours in Bulb mode(assuming full battery at 73°F). If you need additional time, the battery grip would provide that.

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Thank you for your answer, it is very helpful, battery is about half of its original capacity (6yrs old), but even half hour exposure would work for me, I have car charger so I will recharge it when it's out. –  webarto Aug 12 '11 at 18:48

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