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I've installed the camera module v2.1, and now I'm trying to make long-exposure photos with it. I seem to get correct results, i.e. the image is bright enough corresponding to the large exposure time, and EXIF tag in it says that it was exposed with the shutter time I requested, but the whole operation takes 10 times longer than the shutter time I chose.

Here's a sample terminal session:

$ time raspistill -n -t 1 -ss 10000000 -ISO 50 -ex off -fli off -awb off -awbg 2,2 -ifx none -ev 0 -dg 1 -ag 1 -o /tmp/test.jpg -set
Camera control callback  cmd=0x48435045mmal: Exposure now 9999764, analog gain 256/256, digital gain 256/256
mmal: AWB R=512/256, B=512/256
Camera control callback  cmd=0x48435045mmal: Exposure now 9999764, analog gain 256/256, digital gain 256/256
mmal: AWB R=350/256, B=565/256

real    1m41.447s
user    0m0.012s
sys     0m0.062s
$ time raspistill -n -t 1 -ss 2000000 -ISO 50 -ex off -fli off -awb off -awbg 2,2 -ifx none -ev 0 -dg 1 -ag 1 -o /tmp/test.jpg -set
Camera control callback  cmd=0x48435045mmal: Exposure now 1999983, analog gain 256/256, digital gain 256/256
mmal: AWB R=512/256, B=512/256
Camera control callback  cmd=0x48435045mmal: Exposure now 1999983, analog gain 256/256, digital gain 256/256
mmal: AWB R=329/256, B=656/256

real    0m20.542s
user    0m0.011s
sys     0m0.048s

Notice how in the two above commands I set e.g. 10 s exposure, and it takes 1 m 41 s of real time, i.e. 101 seconds, and similarly 2 s exposure takes 20 seconds of real time. And the EXIF tags still report exposures of respectively 10 seconds and 2 seconds.

What am I doing wrong here? How can I make n-second exposure take about n seconds instead of 10 n seconds?

Added:

I've made an experiment where I took a photo of my screen showing output of

while sleep 0.1; do echo -n "$(date +%S.%N | sed 's@\(....\).*@\1@') "; done

while simultaneously running raspistill with time printer in another SSH session:

for((i=0;i<200;++i)); do sleep 0.1; date +%H:%M:%S.%N; done & time raspistill -n -t 1 -ss 2000000 -ISO 50 -o /tmp/test.jpg -set

What I got from this latter command is the following (irrelevant lines skipped):

19:14:18.749608294
19:14:18.863810345
 <...skipped...>
19:14:30.561617727
19:14:30.676428157
Camera control callback  cmd=0x48435045mmal: Exposure now 1999983, analog gain 256/256, digital gain 253/256
mmal: AWB R=456/256, B=397/256
19:14:30.791546552
19:14:30.905176266
 <...skipped...>
19:14:35.004923264
19:14:35.122647672
Camera control callback  cmd=0x48435045mmal: Exposure now 1999983, analog gain 256/256, digital gain 256/256
mmal: AWB R=457/256, B=395/256
19:14:35.238589183
 <...skipped...>
19:14:36.018818862

And the photo looks like this: photo from raspistill

So we can see that actual exposure is indeed about 2 seconds (another photo with a brighter console makes it easier to see the first several cursors, I won't post it here), and it starts roughly 2 seconds after the first callback call. I still wonder what the system is doing before this – and how to remove this delay.

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