Noise on long exposures at night

Discussion in 'General Technical Discussion' started by Elf_8, Sep 30, 2005.

  1. After I had seen some interesting work involving a technique where one paints a scene with a flashlight at night time, I decided to give it a try. To allow enough time to move around, I closed my lens to f8 and took several pictures with exposures ranging from 1 to 2 minutes. I also set the noise reduction to on.
    Back home, I was shocked by the huge amount of hot pixels that spotted the pictures. What would it have been if I had not activated the noise reduction ? I am now about to consider that long exposures at night (1 to 2 minutes) is out of the range of possibilities of a digital sensor and that flashlight painting photography is still a matter of film. What do you think ?
     
  2. Gale

    Gale

    978
    Jan 26, 2005
    Viera Fl
    Well Christian,
    I am sorry to hear that...There must be a real trick to that.

    Maybe doug Barber will wonder by and help out here.

    They make gorgeous images, made that way.
     
  3. And here was me thinking that all the coloured spots in my long exposure night shots were stars :eek:
    50078592.

    10secs at f4 12-24 at 12mm D1H
     
  4. MontyDog

    MontyDog

    Jan 30, 2005
    #1064 - You have an error in your SQL syntax;
     
  5. MontyDog

    MontyDog

    Jan 30, 2005
    #1064 - You have an error in your SQL syntax;
     
  6. I think the D2X does long exposures amazingly well.

    I have done quite a few from about 20 seconds up to about 90 seconds, and most are pristine. I do use the long exposure noise setting, which clears out any hot pixels.
     
  7. Here is one that I would complain about :
    [​IMG]
    Nikon D70
    2005/09/29 20:18:28.2
    Compressed RAW (12-bit)
    Image Size: Large (3008 x 2000)
    Lens: 18-70mm F/3.5-4.5 G
    Focal Length: 18mm
    Exposure Mode: Manual
    Metering Mode: Multi-Pattern
    94.20 sec - F/9
    Exposure Comp.: 0 EV
    Sensitivity: ISO 200
    Optimize Image: Custom
    White Balance: Incandescent
    AF Mode: Manual
    Flash Sync Mode: Not Attached
    Color Mode: Mode IIIa (sRGB)
    Tone Comp.: User-Defined Custom Curve
    Hue Adjustment: 0°
    Saturation: Enhanced
    Sharpening: Normal
    Image Comment:
    Long Exposure NR: Off


    From the EXIF you can see that Long Exposure NR was... off !
    Now, I did (I'm positive) activate the NR function from the menu. I'll just have to go back for another try.
    Know your gear...
     
    Last edited by a moderator: Oct 1, 2005
  8. Gale

    Gale

    978
    Jan 26, 2005
    Viera Fl
    Christian !!!!!!!!!!!!!!!!!!!!!!

    ...............THATS BEAUTIFUL.................

    Little clone toooooool in PS and all gone spots :>))))))))))



    Ps.. Ya gotta believe Doug Barber had his fingers in PS to finsh his off :>)))

    Oh hi Doug, lololol

    PSS...think Jarrell Connely mentioned one time... Don't ever think my pointy finger wasn't in PS.. (or to that effect :>))
     
    Last edited by a moderator: Oct 1, 2005
  9. I too had written off long exposures... but then...

    Last year, I took some long exposure shots at the grand canyon 2 and 3 minute type exposures. I had the noise reduction (long exposure noise reduction) turned on. The shots looked great on my LCD, but when I got home I was severely dissapointed with the results of the noise reduction. There weren't too many hot pixels, the algorithm had gotten those, but unfortunately, it looked like the algorithm applies the simplest of dark current adjustments. It takes a dark current picture and simply subtracts it so almost all of my hot pixels became dead pixels. The shots languished on my hard drive for a year. Finally, on a whim, I opened them with ACR (my normal workflow used NC4 as my first step), and low and behold it took care of the dead and hot pixels perfectly (and automatically). It seems to have a smarter algorithm, automatically detecting hot/dead pixels and "borrowing" the information from the surrounding pixels. It works VERY well. I only had to do some very minor touch up work and the pics turned out wonderfully. I now have no reservations about taking long exposure shots. Leave the long exposure noise reduction on to take care of the non saturated pixel dark current, then simply open with ACR. Here's the results (you may have seen them in the landscape forum recently):

    original.

    original.

    I don't have any "before" versions, but trust me, I deemed these shots useless, now they're completely saved. Give it a try.

    Dave
     
  10. Dave, you can easily distinguish between stars and hot pixels as the stars are much closer than the hot pixels :confused: . Ehr... I mean the stars will leave a trail in the image while the hot pixels will stick where they are.
     
  11. Wow, these are great ! I figure from the movement of the stars that the first one was taken aiming North.
    Thank you for your detailed solution. I'ill use it in my next experiment.
     
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