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Thread: Long exposure noise reduction.

  1. #1

    Default Long exposure noise reduction.

    Hi guys,


    I'm new and have some questions about this.


    I'm using a Canon 7D. It has this function called "Long exposure noise reduction"

    The problem i am facing now is that, if i turn this on, and if i do a long exposure......

    For eg, 60 seconds..., then the shutter will open and close for 60 seconds, then take another 60 seconds to load the picture. It takes twice the time for a picture to load. Does this happens to u guys as well?
    And also... If u turn it off, the picture will appear in 60 seconds straight after shutter closes.

    However, i realise, for pictures over a few seconds, if i don't turn this on, then i start to have white/blue/red dots that are bigger, then small small white dots everywhere(refer to pic). Is this due to the reduction that is turned off? Or are they hot pixels, or are they dust?

    Is there any way i can go about solving this? Below is a picture of it without turning on this "Long exposure noise reduction" function.

    Last edited by - Zeto -; 7th August 2010 at 11:14 PM.

  2. #2
    Moderator daredevil123's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by - Zeto - View Post
    Hi guys,


    I'm new and have some questions about this.


    I'm using a Canon 7D. It has this function called "Long exposure noise reduction"

    The problem i am facing now is that, if i turn this on, and if i do a long exposure......

    For eg, 60 seconds..., then the shutter will open and close for 60 seconds, then take another 60 seconds to load the picture. It takes twice the time for a picture to load. Does this happens to u guys as well?
    And also... If u turn it off, the picture will appear in 60 seconds straight after shutter closes.

    However, i realise, for pictures over a few seconds, if i don't turn this on, then i start to have white/blue/red dots that are bigger, then small small white dots everywhere(refer to pic). Is this due to the reduction that is turned off? Or are they hot pixels, or are they dust?

    Is there any way i can go about solving this? Below is a picture of it without turning on this "Long exposure noise reduction" function.
    I always turn off Long Exp NR. I will do my NR in PP.

  3. #3
    Member hkingx's Avatar
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    Default Re: Long exposure noise reduction.

    yeah. same as my 50d. =D

  4. #4
    Senior Member wildcat's Avatar
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    Default Re: Long exposure noise reduction.

    Noise is noise. However I don't know why there are so many solid white dots. Could be hot pixels... they look a bit too solid to be noise.

    Suggestion: try to take another pic, or different orientation.
    If they are hot/dead pixels, the spots should appear at the same exact spots. You may have other pictures to compare with.

    I have one red dot on my camera that normally appears during LE, and it's always on the same spot. I don't use LE noise reduction though.

  5. #5
    Member hkingx's Avatar
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    Default Re: Long exposure noise reduction.

    those are hot-pixel

  6. #6
    Member hkingx's Avatar
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    Default Re: Long exposure noise reduction.

    dude, dont worry. learn to live with it.

  7. #7
    Senior Member wildcat's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by hkingx View Post
    dude, dont worry. learn to live with it.
    Wow, you can live with that many hot/dead pixels? I have one and I'm like already.

  8. #8

    Default Re: Long exposure noise reduction.

    There is a few constant red/blue/white dots so far i noticed at the same place.

    However, it only appears if u expose over 60 seconds.

    If not, it doesnt appear.

    Is this the sensor problem, or the lens problem? or the filter problem? I have a ND filter
    Last edited by - Zeto -; 7th August 2010 at 11:43 PM.

  9. #9
    Moderator Octarine's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by - Zeto - View Post
    There is a few constant red/blue/white dots so far i noticed at the same place.
    However, it only appears if u expose over 60 seconds.
    If not, it doesnt appear.
    Is this the sensor problem, or the lens problem? or the filter problem? I have a ND filter
    Lens: elements are moving and the sharp image only appears at the sensor. Everything in front is blur. Unlikely that this will cast such a sharp dot-like image on the sensor.
    Filter: Further away from the sensor than any lens element. Even a finger print will not show up in your images. You could simply remove it to test.
    Google / Search here for 'hot pixels'.
    EOS

  10. #10
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Long exposure noise reduction.

    If I remember correctly, Long Exp noise reduction causes the camera to take another exposure which is of equivalent duration as the original exposure.
    The 2nd exposure is completely dark, and reveals the location of the hot pixels, which the camera's processor will subtract from the original exposure.

    Long Exp NR doesn't remove signal noise.

  11. #11
    Senior Member wildcat's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by ZerocoolAstra View Post
    If I remember correctly, Long Exp noise reduction causes the camera to take another exposure which is of equivalent duration as the original exposure.
    The 2nd exposure is completely dark, and reveals the location of the hot pixels, which the camera's processor will subtract from the original exposure.

    Long Exp NR doesn't remove signal noise.
    Hmm... interesting enough KR and DP has articles on these, and you're right! It would explain why a hot pixel can have it's noise reduced using LENR (which is different from high ISO NR).

  12. #12

    Default Re: Long exposure noise reduction.

    Want extreme long exposure with no noise?

    Your answer is here: http://thaiastro.nectec.or.th/hypermod/

    Not for the faint hearted...
    Canon 5D Mark II | 24-70mm f2.8L | 50mm f1.2L | 85mm II f1.2L | 580EX II

  13. #13
    Moderator daredevil123's Avatar
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    Default Re: Long exposure noise reduction.

    TS, I think you have a problem with the sensor overheating.

    When long exposure, some pixels overheat and hot spots appear. 60s shouldn't be causing this problem. Usually when photographing star trails we sometimes see this if we do 30min exposures or something. You need to bring your camera to CSC to get them to look at this. I really hope you still have warranty on the your 7D.

  14. #14

    Default Re: Long exposure noise reduction.

    for crying out loud, please don't post such large pictures - just the crop of the area with the hot pixels will do.

  15. #15
    Senior Member Numnumball's Avatar
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    Default Re: Long exposure noise reduction.

    Long Exposure NR is simply redundant, i see no diff with it or without it.. If there's a need to reduce noise, there's likes of noise ninja amid some others pp software..
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    Member hotwork77's Avatar
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    Default Re: Long exposure noise reduction.

    That's a lot of hot pixels you got there. Since it is still under warranty, you might want to bring it in to CSC for them to take a look.
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  17. #17
    Member jsprtan's Avatar
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    Default Re: Long exposure noise reduction.

    Hot pixel is always there even on new camera and at factory they will do a cmos mapping as part of the process. From what I read, any thing longer than 2 to 3 sec they will show up. What I think u can do is to do a cmos remapping. For canon, u can do this by first removing ur attached lens and caps up. Go to the menu and under one of the spanner icon there is sensor cleaning menu, Select manual cleaning and the mirror will lock up. Let it run for a minute or longer and after u are done turn off the camera. On completing, the camera will do a cmos remapping and it might help u remove the hot pixel.

  18. #18

    Default Re: Long exposure noise reduction.

    Quote Originally Posted by wildcat View Post
    Hmm... interesting enough KR and DP has articles on these, and you're right! It would explain why a hot pixel can have it's noise reduced using LENR (which is different from high ISO NR).
    A very informative thread indeed

    Have been experimenting with long exposures of late with ND110 and came across this issue as well and I'm having a hard time with the noise reduction process, especially for those exceeding 60secs in exposure. Currently using NR feature in DPP but always end up with pictures losing sharpness and details.

    What do they mean by 'Manually cleaned image' at the end of the article? Cloning?
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  19. #19
    Senior Member wildcat's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by mimik07 View Post
    A very informative thread indeed

    Have been experimenting with long exposures of late with ND110 and came across this issue as well and I'm having a hard time with the noise reduction process, especially for those exceeding 60secs in exposure. Currently using NR feature in DPP but always end up with pictures losing sharpness and details.

    What do they mean by 'Manually cleaned image' at the end of the article? Cloning?
    Maybe I should start switching my LE exposures on again. Someone said my D5000 photo got a lot of noise

  20. #20
    Senior Member ZerocoolAstra's Avatar
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    Default Re: Long exposure noise reduction.

    Quote Originally Posted by wildcat View Post
    Maybe I should start switching my LE exposures on again. Someone said my D5000 photo got a lot of noise
    seems like a lot of people still confused between high ISO noise and the sensor noise (hot pixels, etc)...

    Your issue now is high ISO noise? try to overexpose slightly and the noise should be reduced, since it will form a smaller component of the entire signal.
    Exploring! :)

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