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I found that using raspistill or Camera py module I cannot set lower speeds than 1/30" (converted to nano secs).
I want manual camera settings ISO = value and ss = value
All is fine in daylights but when lower speeds are needed I cannot set them slower than 1/30", they are automatically set to 1/30" or so.
If I only set an ISO value, shutter speed is auto set to lower values like 1/15" or less.
Is this a bug or there's something I am missing?
Thank you

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    If I understand correctly you're wanting longer exposure times (i.e. that's what you mean by slower speeds)? If that's the case you need to drop the framerate of the camera (exposure time is limited by framerate - worth reading the rest of that chapter too for lots of info on how the camera operates) – Dave Jones Nov 3 '17 at 11:43
  • That's right, longer exposures. So despite I am not filming I must to reduce framerate, for example "-fps 2" to set fps to its minimum (as I read in user manual) 2 fps. 2 frames per seconds means I cannot set exposures longer the 1/2 sec or 500000 nano secs. Is that so? I've read that 6 seconds (6000000 nano secs) is the longest exposure time possible , only in auto ISO & speed? – dstonek Nov 3 '17 at 15:46
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    The 2 fps I give in that chapter is for a hypothetical example (that whole first section is hypothetical but gives an overview of how rolling shutter cameras work). The Pi's v1 camera module can do 1/6th fps and thus 6 sec exposures, while the v2 camera module can do 1/10th fps and thus 10 sec exposures. The table later on in the chapter gives the limits of the various modes. – Dave Jones Nov 3 '17 at 15:48
  • I'm still stuck. -fps --framerate is an option for raspivid but I am not filmming, I'm using raspistill (photos - slow speed - long exposures) – dstonek Nov 3 '17 at 16:25
  • Ah, if I recall correctly (been a while since I looked at the code) raspistill sets an "auto" framerate on the camera (it's a little more complex than that but anyway) so there's no need to specify it with raspistill (just the python module). However, you will need to increase the capture timeout significantly due to the requirement to gather frames for AGC and AWB, so try something like "raspistill -ss 6000000 -t 30000 -o long_exposure.jpg" for a 6 second exposure. – Dave Jones Nov 3 '17 at 16:31

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