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I have a Canon 450D Rebel XSi and have been taking some long exposure photos. I am finding that with the weather being sporadic lately I need to pack up my camera before the exposure has completed. Will it hurt my camera to turn it off during a photo while the shutter is still open? When I switch the camera to Off during the exposure it says that it's still recording. If turning the camera off is a bad idea, are there ways to end the exposure early so that it can start processing the photo while I put the cap back on and pack up?

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Yup, just hit switch the power button to off. No problem. –  dpollitt Jul 15 '13 at 1:23

2 Answers 2

Since you are talking in the context of long exposure shots, there are two possible scenarios when Long Exposure Noise Reduction (LENR) is enabled:

1. The shutter is still open and recording the scene. In this case, if you turn off the camera the shutter will close immediately and the exposure in progress will be recorded. No LENR dark frame will be recorded. There will be a short delay before the camera is completely powered down, but it will be completely safe to go ahead and move the camera and remove the lens during this time.

2. The shutter is closed and Long Exposure Noise Reduction (LENR) is recording a dark frame. In this case, if you turn off the power during the recording of the dark frame, the camera will complete the dark frame and save the image before powering down. It is completely safe to go ahead and move the camera and remove the lens during the recording of the dark frame, as the shutter is closed.

If Long Exposure Noise Reduction is not enabled, turning the camera off when the shutter is open will result in the shutter closing immediately and the image being saved before the camera is completely powered down. It is safe to go ahead and move the camera during this time.

Please note: In all cases the EXIF data will reflect the selected shutter speed and LENR option selected at the beginning of the exposure, not the actual time the shutter was open or whether a dark frame was actually generated and applied to the photo.

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When I switch the camera off and it's recording with the shutter open nothing happens. The camera continues to try to finish taking the picture and I am still left trying to get it to stop. The only conceivable way of ending the exposure is to open the SD card door (which is designed to make the camera shut off), or to pull out the battery. My real question is if I do either of those things will it harm the lens or the camera? It seems my only other real option is to put the lens cap on the lens and let it finish, as was mentioned by AJ, which I ended up doing the other night. –  Mathew Beckman Jul 14 '13 at 20:30
    
@MathewBeckman I do not have a Rebel XSi to test, but the behavior outlined in my answer is identical in my Canon 50D, 7D, and 5DII. If the shutter is open you should be able to hear it close. If the shutter is already closed, the LENR will complete the dark frame before the camera will shut down. –  Michael Clark Jul 14 '13 at 20:55
    
Opening the SD card door while the camera is writing to it is not recommended as that could corrupt the card and you might loose other images on the card. Ditto for opening the battery door while the red light indicating writing to the card is on. –  Michael Clark Jul 14 '13 at 20:57
    
That's what I thought, but I wouldn't be removing the SD card - only opening the door. And I understand what you are saying but it sounds like with those methods I still have to wait for the exposure to finish and I can't stop it prematurely, but the only thing I can do is put the lens cap on and deny the camera any more light. If it starts to rain I can't wait for the exposure to finish. I understand that once the exposure has finished and the image is processing I can pick it up and go, but what remains unclear to me is what I can do to stop an exposure that won't harm my camera. –  Mathew Beckman Jul 14 '13 at 23:02
    
Turning it off does not close the shutter - it does not turn off. It continues with the exposure. –  Mathew Beckman Jul 14 '13 at 23:02

If you want to be able to store the data, you have to end the exposure and let the camera save the information before you turn it off, some cameras may do this automatically when you flip the switch, though pulling the battery wouldn't be able to finish. It shouldn't do any damage to just power it off, but without power, the sensor is going to discharge and any image data will be lost unless the camera saves the incomplete exposure.

You don't have to turn the camera off to move it either. If for some reason you can't end the exposure, simply putting on the lens cap and taking it with you while it is still exposing should be ok and won't contribute additional light to the image, though the image would be fairly dark since it wouldn't be fully exposed. You could stack multiple images together though to correct for this as long as the shots are the same.

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1  
The camera will save the data collected before powering down, at least my 50D, 7D, and 5DII do. –  Michael Clark Jul 14 '13 at 13:59
    
Yep, the power switch on a system camera is not like a light switch at home. Camera will perform certain processes after it notices the user has told it to shut down = turned the power switch to Off position. –  Esa Paulasto Jul 14 '13 at 14:58
    
@MichaelClark - good to know, updated answer accordingly. Only time I've had it turn off mid-exposure is when I've been out of battery, so it never occurred to me to try it. –  AJ Henderson Jul 14 '13 at 21:07

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