Digital "noise" - effect of shutter speed

Discussion in 'Digital Photography' started by Neil Bell, Jul 17, 2003.

  1. Neil Bell

    Neil Bell Guest

    Mt question is probably simple for most of you:

    Do you get more noise if you use longer shutter speeds - say 6 or 8
    seconds for example? It seems to me that I do...

    Any help appreciated.
    Neil Bell

    For e-mail replies remove the "notreally."

    |------------------------------------------------------|
    |"The greatest peril faced by all people is a failure |
    | to question and challenge religious dogma" |
    |------------------------------------------------------|
     
    Neil Bell, Jul 17, 2003
    #1
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  2. Neil Bell

    Luke Guest

    There are actually a lot of factors that come into play here, but looking at
    it in the most simple terms:

    If you have a long exposure you are letting less light in (either because
    there is less light available or you have incresed the f number).

    If you have less light coming in the signal detected in dark areas of the
    image will be closer to the noise floor in the detector (known as dark count
    or dark current). This gives more noise in dark areas or otherwize you lose
    the dynamic range in the image.

    With longer exposures a greater signal builds up from the dark current this
    limits the dynamic range available for the image signal so any errors
    (noise) on the pixels represents a greater part of the of the dynamic range
    available for the image.

    There is more to it but these are the basic problems.

    So in short you are right you do tend to get more noise with longer
    exposures.

    Many cameras will employ noise reduction above a certain exposure time. This
    is like taking an exposure without opening the shutter, it allows the camera
    to better determine where the black level should be but it doesn't get round
    the fact that you are left with less dynamic range available in the detector
    to store the image in.

    Luke


    "Neil Bell" <> wrote in message
    news:...
    > Mt question is probably simple for most of you:
    >
    > Do you get more noise if you use longer shutter speeds - say 6 or 8
    > seconds for example? It seems to me that I do...
    >
    > Any help appreciated.
    > Neil Bell
    >
    > For e-mail replies remove the "notreally."
    >
    > |------------------------------------------------------|
    > |"The greatest peril faced by all people is a failure |
    > | to question and challenge religious dogma" |
    > |------------------------------------------------------|
     
    Luke, Jul 17, 2003
    #2
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  3. Neil Bell

    Mxsmanic Guest

    Neil Bell writes:

    > Do you get more noise if you use longer shutter
    > speeds - say 6 or 8 seconds for example? It seems
    > to me that I do...


    Yes, usually. Noise in a digital camera is a function of temperature
    mutliplied by the duration of the exposure, so if the temperature goes
    up or the shutter stays open longer, noise increases.

    In early cameras, and still today in many cheaper cameras, thermal noise
    is bad enough to make long exposures problematic. High-end cameras with
    large sensors (which are less vulnerable to noise) do much better.


    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
     
    Mxsmanic, Jul 17, 2003
    #3
  4. Neil Bell

    MarkH Guest

    Neil Bell <> wrote in
    news::

    > Do you get more noise if you use longer shutter speeds - say 6 or 8
    > seconds for example? It seems to me that I do...


    On a Canon 10D the best bet is to use ISO100, I get no noise visible, even
    for a 30 second exposure.

    Here’s a 15 sec exposure:
    http://arrdee.net/~flyinass/markpics/Web/Stuff/IMG_2699a.htm






    --
    Mark Heyes (New Zealand)
    See my pics at http://homepages.ihug.co.nz/~markh/
    "There are 10 types of people, those that
    understand binary and those that don't"
     
    MarkH, Jul 17, 2003
    #4
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