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Most DSLRs have an exposure time limit of 30 seconds. Now I'm asking myself how is it possible to create images about over 1 hour or longer, like these two:

(I have a Canon 60D)

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possible duplicate of Long exposure on Canon 60D –  mattdm Mar 25 '12 at 21:29
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4 Answers

up vote 13 down vote accepted

Yes it is possible with all DSLRs.

The 30s limit of all non-Olympus DSLRs is for timed exposures, meaning you dial in the time ahead of time and the exposure takes up to 30s (or 60s for Olympus).

All DSLRs also have a bulb mode which you press the shutter to start the exposure and let go when you are done. This can also be done with a remote control which is highly recommended to avoid shaking the camera during the exposure.

Bulb modes also have limits but manufacturers do not all publish what it is. For Olympus and Panasonic, this is known to be 30 minutes. Some cameras can take a single exposure of several hours. Regardless of the model you are always limited to the battery-life of your camera unless you use an AC-Adapter and have somewhere to plug it in.

Digitally you can simulate extremely long exposures using Exposure Stacking which basically adds up multiple exposures to make a longer one. A lot of astro photography is done that way, just make sure that your camera does not apply Dark-Frame subtraction between shots otherwise you will have gaps in your star trails. On some cameras you can disable Dark-Frame Subtraction but not on all.

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Worthy of note is that some remote controls have just a simple button that you have to hold down for the duration of the exposure. Others have a locking mechanism to hold down the button (so you don't have to hold it for 30 minutes), and others are really advanced with build in electronics so you can program a specific exposure, or if you are doing time-lapse, program it to create an exposure at specific intervals. –  Pete Mar 26 '12 at 7:21
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In addition to the good stuff that @Ital wrote, you should know that when doing very long exposures with a digital camera, the sensors can over heat and self-generate noise.

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Furthermore, some cameras will automatically cut-off the exposures when the internal temperature gets too high. –  Itai Mar 25 '12 at 20:32
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Just because the upper limit shown is 30 seconds doesn't mean that's the longest exposure you can make without a bulb.

I have been experimenting lately with low light HDR images. My base exposure on one was f/5.6 at 10s. I set my camera up to make a total of 5 exposures, at two stop intervals. It successfully exposed photos at .6s, 2.5s, 10s, 40s, and 160s. All without using bulb.

30s is the longest base exposure I can set up. With 3 stops between each one, my camera will automatically take a 2048s second exposure (34 minutes) without using a bulb. I'm not sure if all cameras will do this. I was pleasantly surprised.

That said, what you really want is a remote so you can manually set longer exposures. I've had this one for a few months, and I'm happy so far:

http://www.amazon.com/Studiohut-Control-Shutter-Digital-compatible/dp/B002IPMQTS

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Indeed, not all cameras do that. Most cap the exposure time at 30s, even with bracketing, so if you try to bracket from a 30s exposure, you can get multiple shots with 30s time (which is kind of silly IMHO). Some will open the aperture to get more light so you may still get brighter 30s exposures. –  Itai Mar 25 '12 at 20:31
    
sweet! What kind of camera do you have Eric? –  Paul Cezanne Mar 25 '12 at 21:25
    
The camera is a Canon 1D4. –  Eric Mar 25 '12 at 22:44
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You could try out the custom firmware Magic Lantern (http://magiclantern.wikia.com/wiki/Magic_Lantern_Firmware_Wiki). I use it with my Canon 550D without any problems. Besides other useful features (intervalometer, audio triggering, motion detection, HDR filming) it has a Bulb mode where you can set the exposure up to 4 hours (as I can remember it).

The custom firmware installs on your SD card and not on the internal memory of the camera. So if you don't like the firmware, just format your SD card and everything is back to normal. Good luck, make sure to read the instructions on the site.

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