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Long exposure processing time

Discussion in 'Image Processing' started by BJTeng, Dec 16, 2012.

  1. BJTeng

    BJTeng TalkEmount Rookie

    14
    Dec 1, 2012
    Hi all I'm new to the nex system
    I try to take a photo of my car at night
    using Bulb for over 10min
    The photo was great but I'm not sure it is normal for the nex 7 to take like more than 10min processing the image
    Thanks
     
  2. applemint

    applemint TalkEmount Veteran

    245
    Sep 20, 2012
    That's the long exposure noise reduction - it will basically take as long as the exposure time again to process. You can turn it off in the setup menu, which is fine if you shoot raw and use noise reduction in post but if you shoot jpeg only your images may be rather noisy. 10 minutes is a very long exposure though - where you taking pictures of a black car in a cave? :)

    I usually shoot jpeg+raw and leave the noise reduction on unless I am shooting something like fireworks where I don't want to miss stuff while the camera is processing, but my 'long' exposures are usually 30 seconds or less with an occasional 1 or 2 minute one.
     
  3. Luckypenguin

    Luckypenguin TalkEmount Regular

    110
    Sep 26, 2012
    Brisbane, Australia
    Nic
    The camera is taking another 10 minute exposure, essentially an image of the back of the closed shutter. In a perfect world this would create a completely dark image, but in reality there will be hotspots on the sensor that were caused by it being active for so long and will show up as noise. These hotspots will be mapped in the second dark frame and subtracted from your first frame to reduce noise. The actual processing time is minimal.
     
  4. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    Whatever, if you turn off long exposure noise reduction (which of course doesn't change your RAW-files anyways) it processes the files lightning fast.
     
  5. Luckypenguin

    Luckypenguin TalkEmount Regular

    110
    Sep 26, 2012
    Brisbane, Australia
    Nic
    Dark frame subtraction (long exposure noise reduction) is also applied to raw files.
     
  6. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    Are you sure? When long exposure noise reduction is turned on and you shoot in RAW only it doesn't take long to process the image.
     
  7. Bimjo

    Bimjo Super Moderator

    Oct 28, 2011
    Washington State
    Jim
    It does on my 5N.
     
  8. Luckypenguin

    Luckypenguin TalkEmount Regular

    110
    Sep 26, 2012
    Brisbane, Australia
    Nic
    Well I can't say for sure with a NEX, but based on other brands of cameras it should also be the case here.
     
  9. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    Okay, just checked again, and you're right. Only question now is - for 10 minute or longer exposures, is it worth the wait? (At -20 degree C, I should add ;))
     
  10. Luckypenguin

    Luckypenguin TalkEmount Regular

    110
    Sep 26, 2012
    Brisbane, Australia
    Nic
    As a test you could put a lenscap (or bodycap) on, place the camera in a dark environment and take a 10 minute exposure. The resulting file will show you how much noise is generated just by the sensor being active for so long. I think that this could be affected by temperature so the results may appear worse if you do this test indoors. A practical test would be to try two identical exposures with LENR turned on and then turned off, and see if you are still happy with the image that was taken with LENR turned off.
     
  11. BJTeng

    BJTeng TalkEmount Rookie

    14
    Dec 1, 2012
    Thanks for the tips guys